Is my girlfriends libido gone forever?

My girlfriend of over 3 years has basically stopped having sex at all with me. In the last 6 months i think we have done it two or three times. Before that we went about 9 months with no sex. Its not only that though, she NEVER lets me please her orally anymore and she will not touch me intimately. Even kissing has degraded to her only ever being passionate when she has been drinking but even then it never progresses and seems like its all a joke. I am 20 and she is 19 and should be experimenting like all her friends and every girl I've had has been far more into me intimately. I really do love her and don't want this to ruin us but its really killing my self-esteem and the level of tension i feel all day, every day is driving me insane. It's getting to the point where i am becoming afraid of what i may do when i snap. I have become jealous of everyone, even her pics on Facebook of her pecking one of her chick friends pisses me off. I don't want this to ruin what we had and still have but i really need some help. PLEASE HELP ME!!!