I'm really confused? Help please?

Ok so my ex and i had been going out for a year and a bit but we broke up at the start of August because she cheated on me. I broke up with her because i couldn't trust her anymore. I really have missed her. Then about three weeks ago she rang me and asked me if we could be friends so I could try and regain her trust. I said ok. Now we're as close as ever, but just friends as she has a new boyfriend, but somehow i haven't been able to move on, and i'm still crazy about her. For the past couple of days she has been flirting with me, telling me how much she misses me, misses what we had, and how much she still loves me. I really want her back but shes with another guy? Any tips on how i can try win her back, or what i can do? If you need more info let me know.