1. Alicia was, undoubtedly, the first he consciously realized he liked. Possibly the fastest brought-on crush as well, but as we all know, that ended terribly. Not that he ever stopped thinking she's pretty.

2. Prior to that, however, there was probably Hanna. They spent so much time together, went through so much, some sort of bond had to have blossomed from that. Granted, neither of them knew what it was, and by the time either of them may have gotten around to noticing what they could have had, everything was broken, anyway. Hanna was changed and Zachary had been stolen by Nick. Even before then, he had stood in their way; Hanna was enamored, Zachary was idolizing, and everyone was fine with that.

3. It wasn't until he became Champion, renovated what laws he could, and found he had absolutely nothing else to do with his free time that he found himself thinking about girls again. And maybe Ike acting so warm to Harlan had something to do with that, too. Maybe.

4. "How are you doing these days?"
"Oh, you know. Running the Gym, visiting Tessa, taking care of my team. Sunyshore has been really quiet lately, thanks to you and Nathan. Not that I'm complaining. Sonya helps out, but I think she's been missing you and him around so much."
"You still visit Tessa?"
"Well... Yeah. Wouldn't you visit your girlfriend if you were in the same city for the first time in over a year?"
"I... don't have a girlfriend."
"Why not?"

5. Anyone who would've known about his sudden interest in girls—or, perhaps, his curiosity, not quite an interest yet—would have immediately thought of Cossette. His team certainly did. He, on the other hand, didn't.

6. Contrary to popular belief, Zachary hadn't always been straight as an arrow. Then again, he hadn't been much of anything for a large portion of his teenage years. Nick may have gotten that ball rolling, if only because he was so unused to attention and joking around and physical contact with other people. But, contrary to even more popular belief, Archie was not the one who first got him to consciously examine his sexuality and where he may or may not lie on the spectrum.
Jude was.

7. "She's too young for me."
"But she likes you. That's pretty obvious. Why don't you give her a chance?"
"She's... too young. I don't want to hurt her."
"Hurt her? What do you think you'll be doing to her?"
"I've already hurt her, Hanna. I don't want to make things worse."
"So you're ignoring her."
"...Yeah."

8. Kisses and hugs had been stolen from him all his life. He was pretty used to it, actually. Well, stolen from him or given to him, but he was always the passive one. He gradually got past hugs and gave them of his own volition, but kissing was another matter. It wasn't until one of the Christmas parties and a confused Vaikuntha kissed him under some mistletoe that he'd had enough. He stomped over to Arianna and pulled her down for a kiss. It wasn't magical like the movies said, and it wasn't even all that great, but damn it, he was the one giving it.

9. Arianna caught his attention when she said she wasn't a trainer. She kept it when he flipped through her sketchbook and found page upon page of his team. It turned out that the way to a boy's heart wasn't his stomach, but his Pokémon.

10. For the same reason, they didn't last. She liked his team well enough, that was true, but she just didn't... get training. Or so he told himself; that was a simple, unavoidable reason. But really, it was a lot of things, as in any breakup. Too much time, too little time, accidents and anger and annoyance, and it boiled down to what he believed was training. He was a trainer. His team came first. And simply speaking, she couldn't accept that.

11. It was only after Zachary's first breakup that he realized how lonely he was in the world. For human companionship, at any rate. He had just a handful of friends and acquaintances that were still speaking to him, but that was his fault. He wasn't terribly social, and running away from everything made it worse. He only had himself to blame.

12. It was inevitable that Cossette would track him down. What was unexpected was that she did it not as a reunion between friends; she faced him as a fellow trainer. And for the first time - perhaps the wilderness had hardened him - he thoroughly trounced her. He expected tears or anger afterwards. Instead, she just acknowledged that she still had a ways to go. That was when she appeared on his radar. She had grown up.

13. He was dancing with Hanna at her wedding when she leaned in and whispered, "Are you going to marry Cossette?"
He denied it, blushed, stuttered, and completely gave himself away. Not that he was thinking about proposing - they had nothing but random battles and hurried kisses and broken French between them - but the fact that there was... potential.
Hanna smiled knowingly and rested her cheek on his shoulder. He had finally gotten more than half an inch taller than her, but he still felt like such a kid around her. She had faced her life and made the changes it needed. He had not. "Go and dance with her tonight, okay?"
"...Fine," he grumbled reluctantly, cheeks still warm.
Hanna released him and shooed him off. Not towards Cossette or anyone else, but just letting him go free. He stood at the fringes of the crowd, uncomfortable in his suit, and watched her twirl about the dance floor with Jude. The dancing reminded him too much of Carlita and no amount of the joy in the air could fix that for him.
He didn't dance with anyone but Hanna that night, but a month and a half later when Cossette approached him again for another battle, he refused her. And it wasn't romantic or sweet, because she stubbornly refused to take his hand and dance then, so instead he picked her up and carried her over to where Ike was napping with his portion of the kids.
"Don't scowl at me like that," he told her, "I don't like it when you do that. You... Look at the cute sleeping babies and smile. You haven't smiled at me in months, Cossette."
She still didn't. "I have not won any battles yet."
"You have badges, and you have a large team again. You've been winning battles."
"Just not with you."
"And you're mad at me for that?"
"Non. I am mad at myself. I want to be your equal."
"So you're challenging the Champion?"
"...No, I am challenging my hero. And he still stands strong." She didn't have to sound so angry about it, though.
Zachary laughed, and he was proud of the fact that it was only a little bitter. "Come here. Teach me French."
It caught her off guard, but she allowed herself to be held as they sat down, using Des as a backrest. "...What is it you want to say?"
"How do I say... You're frustrating, and stubborn?" She elbowed him, hard, in the stomach. "Fine, how do I say you're cute?"