<human>: Condense the text into a few key points

Although i originally typed up something stupidly long i'll give you the short version: 
Im 27, Male, and dont live at home. a girl moved in with one of my neighbors/best friends (w/his parents & siblings, not just him) about 7 years ago. fast forward 4 years of getting to know her and we hook up, eventually begin a relationship.

Over the past two years and a half years she's opened me up to new things, gave me confidence i was lacking, and in general altered my life for the better. But now im beginning to wonder if i made a mistake by getting into such a good relationship so quickly. She's not my first sexual partner but she is my first relationship. With the new-found confidence i've been wondering lately what could be, thinking that if i dont get out soon im going to pass over my youth and miss out, potentially resent being with her down the road.

I've been feeling conflicted over this for the past couple weeks, gradually wondering more and more of what to do. And as if to pile on the temptation, while i was killing some time at a BestBuy last weekend a very cute girl approached me and gave me all the signs she was interested, even as far to ask 'is there anything you wanna ask me' a couple of times. (Believe me i wanted to, but im not a cheater, thats unfair to both of them)

My Question: 
Do i stick it out, hope the feelings subside and live life wondering what could have been and possibly resent being with her later on? or do i break off a great relationship (that is a close friend to everyone i know and lives with one of my best friends) for no reason and risk never being in one again for the -chance- of meeting new women and a who-knows-what outcome with my friends? My decision wont be easily swayed, but either choice has such implications for shaping the rest of my life that i cant make sense of it all anymore. I wish i could pull a Multiplicity and live two lives.. but living in the real world i cant decide who i'd rather be (or rather, should be).

Still
<bot>: Im 27, in a relationship thats doing great with a fantastic girl but im beginning to regret that she's my first girlfriend and i might miss out on the opportunity youth has to offer. Do i leave or work it out?