pooh, how into his girlfriend is he? If he is in love with her, that is a problem.
You have a good thing going with him. I had a little buddy, who was younger than me, too. I lived in a house for many years with a bunch of other people. My little buddy moved into the house when a room became available. I loved this guy. He was so smart and funnier than hell! Cute, too. He also had a big dick. I found that out one morning when we had plans and he was a lazy ass and wouldn't get out of bed. I finally bitched at him enough that he threw off his blankets and stood up. He was wearing boxers, but didn't have morning wood. He had morning lumber! Damn he was hung! Small guy with a big dick. He just grinned at me and walked past me to shower. I'm sure my mouth was hanging open.
Another time I was home alone watching porn. He came home just about the time I was about to strip down. I remember him standing behind the couch, watching porn with his hand in his pocket! LOL! I so wanted to ask him to join me.
Another time we pooled our money and planned to call an escort service. He said he wasn't going to fuck in front of me, but I thought to myself, I will go first in front of you! LOL! Our roommates came home drunk, so that never happened. Damn it!
He knocked up his girlfriend and moved out. Yeah, I do regret what could have been, but I didn't want to lose the friendship either.
Hell, you are already more than half way there!
You have stirred up a perv nest!