I'm torn between two guys.

ok well I was in a relationship with dave for about a year and a half. I was moving a half hour away and he didnt trust me to be at a different high school. I wanted to move to be with my mother and brother. We were wayy too close and spent every second together, however, he was always there for me and loved me soo much. Then, right before I moved, things were getting rocky with dave. I ended up cheating on him with a past friend, timmy. Tim was more attractive, mysterious, and deep. Once I met him, I couldnt wait to move. He did tell me he was in an alternative school with “crazy people” I didnt care. I wanted to know everything and was so excited to have a nw fling. me and dave broke up, he threatened to kill himself etc. then we just didnt talk. I have been with tim for 3 months now and he has already kissed another girl and went away to a youth center for 20 days. I know hes unstable and unpredictable but who likes predictable? I had some problems with tim lately and called dave. he broke up with his girlfriend and we planned to go back out. I then decided to take tim back after he called in tears twice. dave is hurting soo bad. I feel horrible and I know its all my fault. I now dont know if tim deserves one last chance. hes begging for a last chance. Hes even going to get bipolar medicine. dave is just waiting and gets mad a lot. heellppp! each want the other completely out of the picture :(