Because I imagine that neither of them would have been quick to say it (especially her). The handshake in the last scene might be real, it might not. I've seen it in movies and researched it; but the answer is unclear. Just please go with it.
Disclaimer: If I was RR, Reyna and Jason's relationship in SoN wouldn't have been so dang misty and unclear and 'come ON just TELL US'.
Just Friends
"Alright, we accept you in the legion." Jason said. "You made good time coming from the Wolf House to here, by the way." The new recruit they'd been interrogating smiled that exhausted 'great, but right now I couldn't care less, have you got a bed somewhere I can use?' smile and thanked Jason in a mumble.
"There's a guy named Bobby waiting for you outside." Reyna said.
"He has an elephant with him, don't freak out." Jason slipped in for the recruit's benefit.
"Yes, the elephant is normal." Reyna said, remindd of the human side of explaining the legion's purpose. "He'll take you to read the auguries and decide if you are to stay or not. Someone will then give you a tour of the fort and answer the questions you have. We will assign you to a cohort that evening, which is when we will give you your armour and probatio tablet."
"Welcome to the legion," Jason said. He was strict still, but he was the humane, connectable and more 'friendly' side of the two praetors. The one that the recruits understood and nodded and were comforted even in the smallest bit by. He reached out to the new recruits better and he was more of a people's person than she was (which wasn't hard in the first place).
"Thanks," the girl said. She was heading towards the door when she turned around.
"You guys finish each other's sentences a lot. Are you guys dating?"
"No," Reyna said. "We're just colleagues. Make sure you remember to mind your own business or you will be punished with consequences you will find most… Severe."
The girl became red all over and her eyes widened like a deer in the headlight before she mumbled something and slipped out.
And if Reyna hadn't been so quick, she might have noticed the face Jason made when she said 'Just colleagues'.
She was walking back from the senate alone, having had to pick up papers and such that Jason forgot (he was being called by Lupa; he had good reasons to hurry up).
She wore her face as its normal mask of steel and 'don't you try and cross me', and her purple cape billowed behind her as she walked. Some retired legionnaires stopped to salute her, and she saluted back.
She turned a corner and heard two girls, college age, talking.
"Yeah, that's what my brother said, and he's in the fifth like Jason Grace was, so I assume that he knows if they're a couple or not…"
She froze and turned towards the girls, trying to harden her eyes furthermore.
"Well, both of them are praetors, and they're frankly meant to be even if they wouldn't be. I mean, I'll always remember how protective of her he was when he first brought her to the fort when they were thirteen..."
"Excuse me?" She said. They both looked up at her and their faces jumped to 'deer in the headlight'.
"He's not my boyfriend. We're just friends." She told the two girls. "I don't know who your brother is, but tell him to stop repeating lies like that before I find out who he is." She said.
The girl nodded.
"Yes Praetor Bell, I apologise, he's only a little boy you know, he gets things screwed up and- and-"
"It doesn't matter." Reyna said. And as soon as she was out of ear's reach, the girl turned to her friend.
"See how defensive she got?"
"Mmm-hmm, they're definitely getting there, your brother was onto something."
Jason had dragged Dakota out of the hall to give him another 'enough with the Kool-Aid' talk. Gwen looked at Reyna with an eyebrow raised, finishing her drink.
"What?"
"Starring at Jason as he walks out," she said very quietly.
"No I'm not." Reyna defended. "I mean, I wasn't..."
"Yes you are." Gwen said.
"Did you know that body language is 55% of how people flirt?" Bobby put in.
"What?" Reyna asked.
"Reyna, look, we know. Okay? You might not know. You might still be in magical stone-heart world. But we know." Gwen said. Reyna had a feeling someone was trying to drag her into girl-talk again.
"For Rome's sake, know what?" Reyna asked, her patience slipping away like water in a sieve.
"That you like Jason." Gwen said lowering her voice.
"Oh no, not you too." Reyna sighed. "Look; I've said it a million times and I'll say it a million times more until people stop being so thick. I don't like Jason. We're just friends."
"Reyna, you have a heart, and that's fine, you're allowed to let it show-" Gwen tried to soothe.
"Every 7 minutes, someone in Canada dies of a heart attack." Bobby put in.
"-It doesn't make you weak or whatever it is you're scared of. Please be honest with yourself Reyna, so this can just move on."
"There's nothing to move on to!" Reyna said. It came out louder than she'd meant it. With a glare most people turned away.
"We're just friends." She whispered to Gwen.
"Did you know that-?"
"Bobby, this isn't time for a statistic on friendship." Gwen said patiently. "Or one on romance." She added when she saw her friend's mouth open again.
"Especially considering there's none of the later." Reyna said. She scraped up the last of her dish and got up as a wind spirit took it away.
"Now if you'll excuse me, I have some work for Lupa to do before the War Games." Reyna said, getting up and leaving.
On her way out, she wasn't paying attention to her surroundings (which was very uncharacteristic of her) and bumped into Jason's shoulder.
Her eyes shot up to see what she'd bumped, and she met his and for a second she was caught in just how blue they were…
"Sorry," he said.
"I wasn't looking." She said. She looked into his eyes for a while longer. It was incredible how much of his was stored in them. The serious, Roman look he'd grown up with, the look with which he looked at everyone and basically sucked out whether they were okay, or if they needed anything…
Before forcing hers away and walking to the principia.
"Of course, I could be wrong. Perhaps the gods sent you here to test my judgement." Reyna said. The look in his eyes was so much like Jason's when he was unguarded… They were completely unlike, she could tell after meeting him less than 24 hours ago, but there was that simple 'I care' factor that she'd never admitted she liked about him. About Jason, that was. She wasn't wrong. "But I think… I think you were sent to here to make up for the loss of Jason." Or try.
"The way you talk about him…" Percy said. "Were you two a couple?"
Her fist closed, nails digging into the wood table. She knew her eyes must be hardening on the outside. Why did everyone ask that? Couldn't they just give her a break on that one thing?
"We might have been," Reyna said. If I'd just talked quicker last time we talked. "Given time. Praetors work closely together. It's common for them to become romantically involved. But Jason was only praetor for a few months before he disappeared." Not long enough for someone with his leadership and battle qualities and skills. "Ever since then, Octavian has been pestering me, agitating for new elections. I've resisted." I've always resisted, haven't I? "I need a partner in power- but I'd prefer someone like Jason. A warrior, not a schemer." You will never replace Jason, Percy Jackson, I don't care how dashing or Prince charming you are to anybody else, but you're as close as I can get to someone who cares and rules well. You're better than Octavian, you're his cousin, and I get the feeling you've done this before at some point; just like him.
Hylla pinned Reyna to a wall, covering well so her sister wouldn't dart away like she knew Reyna could do.
"What?" Reyna asked, annoyed.
"Why are you walking away from the feast?"
"I need air," Reyna said. "You know I don't like to feel cornered since Blackbeard."
"Yes I do." Hylla said. She looked at her sister for a few seconds before bringing it up. "That Jason Grace boy that everyone's been talking about," Hylla said. "He was the other praetor."
"Yes," Reyna said. "I know."
"Praetors become romantically involved. You guys were just friends, right?" Hylla checked. Reyna didn't say anything, she just looked at Hylla.
Hylla raised an eyebrow, Reyna crossed her arms.
Hylla put her hands on her hips, Reyna shook her hair back.
"Someone's going to have to talk." Hylla said.
"Maybe we were, maybe we weren't." Reyna said.
"And you are being skirty and avoiding about this because..?"
"Because I don't know," Reyna finally said. "I mean, he disappeared, and I didn't have a chance to say anything to him when I was about to because Vitellius –curse him- just popped out and told us to do our duties as praetors and show some responsibility and respect curfew, and we can't argue with Vitellius, because that just isn't done and…"
She took a deep breath to calm herself, to regroup all the pieces scrambling broke her into. "So in all due respect, I guess we are just friends."
"But you don't want that." Hylla said. Reyna sighed and looked up at the sky. She knew Jason wasn't going to just drop down from it. At least not tonight. And there was no guarantee that she'd be anything other than just a friend when he did.
"The last eight months I've been torturing myself about how I should have told him before. I've always said 'just friends' and maybe he's believing it too badly now."
"He likes you?"
"Gwen says he did." Reyna said. "I don't know about now. He's liked me for a long time, according to her and... Well, he might be tired of waiting."
Hylla pushed her sister's bangs from her face. She pushed it back down to hide a cut she'd made the healers skip by so they'd look after her men first. One of those tiny feats that did show to anybody who challenged it that Reyna did care.
"You know what, I have no romantic experience, and although I'm slightly ticked that my little sister is beating me to it; if you really feel this strongly about him, there's no way he considers you 'just a friend'."
She watched him jump off the ship, ignoring the board linking it to the ground since he always landed on his feet anyways. She had to force her feet not to run towards him like Percy had ran to Annabeth.
A huge roar exploded from the crowd of legionnaires, senators, and even just the citizens of New Rome when he landed on their land again. Jason raised his hand in salute, and Reyna couldn't help it, she strode forwards and gripped his forearm as greeting. His hand closed around hers, and she allowed herself a smile.
"Look who came back," she said. He grinned and the scar above his lips turned into a crescent, like the moon.
"Yeah," he said. She threw her other arm around his neck and he was startled at first, but he hugged her too.
"So I guess that what you would have said if Vitellius hadn't come along was that we weren't just friends? Because I've been holding onto that, and meaning to ask, for the last eight months." He whispered in her ear. She was so surprised she just stood there in shocked silence, in his arms.
He remembered. He brought it up. Hylla had been right. He… Her heart started beating fast, with something other than battle adrenaline.
"Seal it with a kiss next time we're alone," she whispered in his ear.
"Can't wait for it, just my girlfriend." Jason said.
Right then when he said that; she didn't think she'd manage to wait to kiss him either.