As you laughed and played with the one you loved, Ace was hurting inside.
He should be the one you were like that with. You were his best friend, after all! But... No. You had to go and fall for someone else. And it's not like Ace could do anything about it. No, he respected you too much. He loved you too much to let you be anything but happy.
He'd tried pushing the feeling down. To tell himself you were just his best friend, nothing more. Because that's what he was to you too, wasn't it?
He was running from himself. And truly, it was killing him.
So while he was a bit jealous, he stood by against the wall, simply watching you and your loved one.
"Hm? Oh, nah, I was just thinking. No worries!" Ace faked a grin when you asked what was up. "Yeah, I'm good. Just go back to your little friend, 'kay?" He waved you off, classic Ace Trappola smile on his face.
When you turned back, he sighed to himself. Damn, I gotta let go.