It's my humble opinion that if you can't accept this girl at her worst, you don't deserve her at her best. Yes, you do need to be attracted to this girl for your relationship to succeed. But um...if she doesn't do it up now, she probably never did -- and you've been together for 3 years? Has she worn a mask this entire time and you're just NOW figuring out what she looks like? Probably not.
No, you're being bombarded with temptation (helloooo, college) and you can't hack it! I'm not trying to insult you guy, it's just the truth. You're basically looking at this girl that's been loyal to you and with you for these 3 years and saying, "You no longer impress me." That sucks -- but, it is what it is.
You need to break up with this poor girl before the both of you waste more time. & if you're having difficulty with that, you need to look EXTREMELY deep inside yourself, and figure out where YOU changed, because from your side of the story, it doesn't sound like she did. She counts on you as a constant in her life, that's not something to be taken for granted, so if you can't find your way around to accepting her exactly as she is 24 long hours of the day, you need end it.
A sniper is the worst romancer, they never make the first move.