I'm mainly straight..I am a woman who likes men...really likes them. But I liked girls growing up too, enough to appreciate looking at them, even today and doing some "experimenting" before I was in my dating/marriage to my husband in my teens. It is totally reasonable to be able to be attracted to one sex, even if you normally gravitate towards the other one. I believe you love who you love, sometimes even when it makes no sense at all. It should never be passed by because it doesn't fit in with a label you or someone else has given you.
That being said, I remember those first relationships..most of them are pretty tame as teenagers, they seem to tend to be more emotional than physical for the most part. I agree with Napervic, even if you weren't in a physical relationship, you were in an emotional one, and your "girlfriend" and best friend betrayed that. That is bound to be hurtful, no matter what, especially if this was your first. And, as to the drink...I still remember why I drank Dr. Pepper for years each time I have one...my first crush then boyfriend influenced my choice since he loved them and that was all he drank. The relationship ended when he "cheated" one me, very hurtful even at a young age since it was my first relationship. I still remember him, his likes, dislikes, things he did..and this is 15 years later...emotional wounds are the hardest to forget..
Hang in there..hopefully some of the answers on here make you feel less alone with this issue...