Developing feelings for childhood friend while in a long-term relationship. What do I do?

Hi,
I am 22 and have been in a relationship with my current boyfriend for five years. We were high school sweethearts and he is the first and only guy I have ever been in a relationship with. Last September, I moved across the country to go to grad school. Needless to say, long distance has never been easy for us (we had to deal with long distance when he moved to another country for a year before), but I have recently come in contact with a very old childhood friend that also happened to move near where I am now. We had not seen each other for years but when we met up again it was like nothing changed. One night, we both got very drunk and fooled around. After that, we began seeing each other even though we both agreed not to get our emotions involved since he knows I have a boyfriend and we would just be friends. He also specifically said he didn’t want a relationship with anybody at the moment.
However, we have been calling, texting, and visiting each other with increasing frequency as of late and I can’t help feeling that there may be something more. Sometimes we just act very platonic – go shopping and joke around, etc. But most of the time it feels like we are actually dating (cuddling while watching movies together, he holds my hand in public, insists on paying every time we go out to eat, just to name a few things). What I’m feeling is probably just an infatuation at this point but I don’t know if I should pursue this (i.e. break it off with my current boyfriend) and see if this goes anywhere or if I should nip this in the bud and stop seeing my friend. I know I can’t keep seeing him if I intend to stay with my current boyfriend and vice versa since it really is unfair to him. I feel guilty enough about this situation as it is right now and don’t know what to do. My best friend thinks that I settled down too early and I’m only feeling this way because I have never been with anyone else before and I should just cut it off with my friend now because she is determined that he doesn’t have any feelings for me and I’ll just end up hurting my boyfriend and myself. I don’t disagree with her entirely either but I don’t know if he has feelings for me or not. I also don’t know if I’m just feeling this way because of the long distance or just my own self esteem issues. I just wanted some third party opinions that are not biased by knowing any of us. What do you guys think? Thanks very much in advance for reading through all of this and for your input. I really appreciate it.

Cheers.