Addison's never felt so many emotions at once. It was honestly very overwhelming, but also refreshing. He didn't know to explain it.
He was overwhelmingly happy with Oliver to the point where he forgets that he was in a committed relationship with him. There's still a part of them scared that he'll find someone else as fast as we suddenly found Cate.
He's still trying to impress him and show him that he's worth his time.
But with the stress of his college acceptance, he ended up letting go of that feeling...for now.
He couldn't care less about Oliver's opinion right now. To be honest, he couldn't give a shit...