How do I win her back?

My ex-girlfriend and I were together for two and a half years. Its been about four months since we broke up. The moment we broke up she started seeing someone else and I found this out about a month later. She lives with one of my good friends so I usually hear how she hasn't been home in a couple days etc etc. We still see each other regularly, in fact we spent every day from Christmas eve to new years together. However when shes not with me I don't hear from her. No text no call if I try to contact her I wont hear back for a couple hours or sometimes the next day. But when she calls I usually go running to her. Picking her up where ever buying her food taking her home, usually spending the night with her. All I do throughout the day is wonder if she will call me and when she does I get this amazing feeling of excitement. She said we broke up because I didn't treat her well. Throughout the relationship I had all the control and I took advantage of that. Now I'm trying to prove to her iv changed. To take me back. It hurts finding out about her and this other guy but there's nothing I can do but stay put. How do I win her back? How do I show her how much I love her? Am I stupid for putting up with this? I have tried to walk away from this many times but she will contact me over and over again telling me how much she needs me and how it will work out in the end. She keeps saying there's something I need to do to win her back but i feel like its all mind games. I also feel like she is always lying to me but I try to pretend like everything is sweet when we're together so she will want to see me again. I could really use some input/advice. Thank you.