I'm really starting to fall for him...but there is a BIG problem, need help on this?

there is this guy, going to call him jay. i met jay about a month of ago in one of my cles, at first he would just stare at me the whole time during cl and not say a word, even out of cl around campus the stares still continued. i admit i became a little infatuated with him and started asking mutual friends about him, turns out he was doing the same about me. one day he finally sparks up a conversation out of the blue with me and we hit it off, i mean we literally stayed in the parking lot talking for 3 hrs straight.i didnt actually give him my phone number till a week after formally meeting because....he has a girlfriend. he has a fckin girlfriend people! she goes to school about 2hrs away but none the less he still has a gf, of a year and a half i might add. last weekend we hung out and things got a tad bit out of hand, we were flirting which turned into wrestling, which turned into biting? and finally ended in some touching...the "touching" i must say was my fault, couldn't keep my hands off that . the next day he called and i apologize for what happen the night before, and we rarely havent spoken about it since then, he brings it up casually at times but that's as far as it goes. the problem is im starting to fall for him....hard. we flirt constantly and im so comfortable with him, i know hes interested in me and i know hes attracted to me but he has a girlfriend and i feel so horrible even being slightly interested in him considering hes already in a relationship....i dont know what to do, i really like him a genuinely just enjoy his company but i feel in due time my feeling are going to grow even stronger.....should i cut all ties now before things get too complicated or just wait and see how everything works out. should i even tell him how i feel? plee help