Heart Broken And Don't Know What To Do Anymore

On June 19th I was dumped over what seems like an excuse. I was dumped because someone spread a rumor stating I was trying to become boyfriend with a girl I didn't even like. My girlfriend eventually heard and dumped me that day she called me asking her to tell her the truth and I did. But she didn't believe me and still dumped me. I didn't deny it in the first place because I knew she should of believed me and not people. So I didn't call her back that same day because I felt I was right the next day I texted her apologizing for what I had never done but she said she thought I didn't care so I apologized from there and we stopped talking for the day. That same Friday she went to sixflags on a field trip with the school. However my best friend told me she was making out with her ex,spent time with him, and called him "babe". My best friend told me and also told me she said she had been back with her ex since the day after we broke up. It bummed me pretty bad because I still cared and loved he so I texted her and asked her how it was at six flags and she didn't say anything. So still loving I decided to believe her and put it aside she says she still loves me and says she misses me and yeah. So I told her to give me another chance, but she always says "I need time" or "I'm scared to get hurt". The funny thing is when I ask how I've hurt her besides the rumor she believed she can't list anything else I don't know wether to believe that she is probably giving me excuse because she really is with her ex or if I'm just paranoid I don't know what to believe and I miss her but I don't know if I should keep waiting or give up and believe my best guy friend (at one point how ever he was obsessed with her)