Boy troubles

Two summers ago I met two boys, both of which I had "crushes" on. I've now been in a relationship with one of them for almost two years and I'm extremely happy. The other is one of my closests friends and I couldn't be happier, I feel as though I've got the best of both worlds! A couple nights ago I was out getting icecream with the friend and he admitted that he had feelings for me a lot that summer and had considered breaking up with his girlfriend for me. I admitted that I liked him too but we agreed that we both love our partners and are happy with being friends. We have always been weirdly close with each other and openly talk about our sex lives and future plans and everything, however recently it seems like he is treating me like a faux-girlfriend (without going too far) while his girlfriend is away at college. I'm perfectly okay with this, however I don't want it to get too far to where I'm uncomfortable or my boyfriend is uncomfortable. My boyfriend understands how close of friends we are but I don't always tell him about how far our conversations go. Anyways, I'm just wondering what you think my friend is looking for (an actual relationship with me or just being better friends) and what to do to make my boyfriend more comfortable with us seeing each other more, etc.