Jealous: I think I like a guy that likes a girl who already has a boyfriend?

[Stella]

We're all students together in a post-grad program where we met a little over two years ago. A group of us have gotten really close over the last couple of years. One of my guy friends in particular is super funny and just draws me to him. What is it about guys with a sense of humour that is just so attractive?! Anyway, there's also my girl friend (Lisa) who is part of circle of friends who is in a three-year relationship with a guy that doesn't go to our school.

Within our group of 7 friends, there are definitely people who have tighter relationships than others. My guy friend (Tim) messages me on Facebook and will text me almost every day (although it is mostly school-related), but I figure he also enjoys talking to me and obviously feels a lot closer to me than some of the others in our circle of friends. He, by the way, is single...and so am I. Anyway, I guess I felt special until I realized that he is just as close to Lisa as I thought he was to me. I know he doesn't like her anything beyond a really good friend, but I'm not going to lie - it does bother me. A lot. Yes, you could say I'm jealous.

I mean, the reality is that Tim and I could never be a couple because we have a ton of differences on so many levels that it would just never work BUT, I'm all for just light-hearted fun flirting because those things make us feel good - or at least it does so to me.
I see the relationship he has with her and it's almost the same relationship he has with me, but I want ours to be closer and tighter. I just want to know how I can help myself not be so jealous and insecure. He obviously likes me as a friend, and I don't want anything more intimate. I guess I just want more attention from him than he gives to Lisa.

I hope I'm making sense!