Wally's side of Artemis being undercover was never really explored in the show, so yeah, I did my best to express what he might've been feeling.

Enjoy!

Wally exhaled, slowly brushing his thumb over the glass. Her photographed smile reflected back at him, lodging a knot in his throat. His heart clenched. As positive a memory as it may have been, now seeing her face merely widened the gaping hole of sadness within him. He knew it was essential for the safety of the Team, of the League, heck, of the entire free world that she go undercover with Kaldur to learn the Light's darkest secrets. But he couldn't neglect the pain of missing her, it only grew stronger with each passing moment. And after years of waking up next to her face every morning, he wasn't sure he could deal with her absence any longer.

The redhead frowned at the photo he currently possessed. Artemis rarely ever let him take photos of her, she rarely ever let anyone take photos of her as a matter of fact, but he'd still managed to sneak this one anyway. She was halfway through devouring one of M'gann's famous homemade cookies, but had stopped in an attempt to rip the camera from Wally's hands. Even though she hated the picture, he found it endearing.

The smile that emerged upon his face was faint, barely noticeable, but it somehow managed to make an appearance anyway. Although it disappeared almost as quick as it came whilst he set the frame onto the table once more.

Biting his lip, he leaned back into the cushions of his old quarters. Nobody had taken residence in his or Artemis' room after they'd left. They both had a sneaking suspicion that Nightwing hadn't permitted any other heroes to. But whatever the reason, Wally was grateful to have somewhere he could be alone with his thoughts while he was here. ...For however long that may be.

His chest began to ache while his mind was further inundated as a result of the overwhelming amount of thoughts of her.

Even with his struggle to push his sorrowful feelings aside, he couldn't rid himself of the heavy heartache that entered his body with each breath he inhaled. Never in his entire life had he been so miserable, and so incredibly sad and deprived of his typical jubilance. The pain of being without her had almost become unbearable. He felt like he was drowning, struggling for breath, yet still managing to intake a miniscule amount. Just enough air to sustain him, just the necessity. But so minimal to still keep him striving for what would be more comfortable, what would allow him to let go of his woes and troubles.

She was that air.

He'd begun to forget the feeling of her fingers tangled in his hair, the way his heart jumped when he laid eyes upon her, and how good it felt when their bodies were in extremely close proximity. It was like the more and more time they spent apart, the more small things about her were suddenly being erased from his memory. And the idea of all of those things slipping away terrified him. He couldn't bare the thought of something so important to him, like the taste of her lips, or the scent of her luscious hair, leaving his mind for however long they would be apart.

After releasing another long sigh, he suddenly sensed another presence in his room. He didn't even have to lift his gaze to recognize who it was. He didn't even have to guess what he was doing there either, the speedster already knew. "I can't do this anymore," he said slowly, his soft voice echoing throughout the space.

Dick took a step towards him. "You know we need Artemis undercover, Wally."

Wally took a shaky breath. "I...I know, I know...I just…" he started, seeming unable to finish his statement without a slight anger lacing itself into his tone, "Why did it have to be her, Dick? Why couldn't Kaldur use someone else?"

Nightwing shook his head. "She was the only choice."

"But we were trying to leave the life behind. Kaldur knew that."

"Kaldur also knows that she can handle herself," the dark haired hero replied. His feet padded closer towards his best friend, seeking to comfort yet instill reason in him. "I know you miss her, KF."

Wally peered up at Nightwing. An infusement of thick sadness and anger were swirling around inside him, and noticeably interweaving themselves in his voice. "We should have never come back," he muttered.

The former Batman protégé placed on hand on each of the other hero's shoulders. "She's doing good work. You should be proud of her."

"She shouldn't even be there at all," Wally replied, shifting himself out from under Dick's grip.

"KF-"

His next breaths felt as though they were daggers slipping down his throat and into his lungs. "I need to be alone."

Dick scoffed. "That is the last thing you need."

Wally clenched his jaw, the anger taking over the reins more so than the sadness now. "Dick."

"Wally-"

"Just...please...leave me alone."

Nightwing's shoulders slumped, a frown emerging upon his features. Although he clearly didn't like the request he was given, thankfully for Wally, he still obeyed nonetheless.

Walking in the opposite direction, he gave his best friend a longing glance before quietly shutting the door.

The momentary rage had now dissipated, leaving Wally with the agonizing hollowness and heartache that had been eating away at him for weeks on end.

When first proposed the idea of Artemis going undercover, of course he had rejected it. Eventually, he had been convinced by both her and Nightwing, but now he couldn't escape the feeling that they had made the wrong choice.

He didn't think it would hurt this much with her gone. He didn't imagine how unbearable missing her was rapidly becoming. After five years he should've known. He should've known better. But now, he was suffering the aftermath of their decision.

Wally reached over and clutched the photo he'd earlier had in his possession. Squeezing his eyes shut, he held it close to his chest. He replayed the sound of her voice over and over again in his head, her telling him that she loved him and she missed him. He longed to tell her that he loved her, too, that he missed her more than she could imagine.

Because right now, he missed her more than anything in the whole world.