The girl I like has a boyfreind need advise please

I met this girl in chemistry last year, well I met her thourgh a friend. Well anyways we started talking and I’ve found out she is a good little church girl. I also had her in gym thats were we mostly talked. I’ve found out who she liked which really hurt but one of the boys that she liked was a boy who teased me when I was younger a bit of a bully and I told her that. She kinda of believed me but she didnt want to I think. Well thorugh out the year I borught her breakfest, she would see me and come give me a hug always sit next to me on the bus smile when I looked at her laugh when I wasnt funny. A year passed and everyday I regreted not saying anything about how I felt about her. Well I heard a couple of friends who liked her also telling me she was dating the guy who teased me. I dint want to believe it I thought they wanted me to get away from her. I stopped drinking and smoking for her but she doesnt know that. Well then I saw a msg that brought back memerios of her going out with him, I wasent sure if they were. I brought it up in coversation with her boyfreind and he confirmed it. That hurt really much I couldnt decide what to do. their was still some comfort that I knew she was a good church girl and I thought she aint kissing him yet but my other friend told me that they are cause she told him. That just killed me, I cant see her cause every time I see her I imagine them making out. What should I do? I had the impression that she liked me but she didnt know that I liked her. What should I do? Should I still be her friend. But once I learned she had a boyfriend I thought of starteing to smoke and dirnk again need to forget about her. Well should I avoid her now or what?