My Ex.....Please help me! i need advice?

Ok so my ex is dating my best friend Kristin. We dated and were in love...like seriously, until my best friend started flirting and then he said he was going to just see if they connected. All her friends liked her with him better so they kept them together, and us apart. So now, I have dreams about them, and my best friend dieing and him kissing me. And of coarse I still have feelings for him but I dont know what you do. We had a trip to hershey park recently and he sat with me...not her. And she said i was flirting with him, but he didnt care! We were in the same group and he rode everything with me, bought me an icee, let me drink from his soda, held my hand when we were scarred and all that stuff. His girlfriend was in a different group. He was with me about to get on the tilt-a-whirl when they all came and grabbed him so i rode alone. Its just insane. Its almose been 5 months of them dating and Im almost positive we could get back together but I want all of your guys's opinions on this whole thing. I would appreciate it alot! Thx!!