What's really going on?

Me (D) and my ex (V) got back together. After almost 3 months of no contact and me making my peace with things, she reached out, apologizing for the things she did, promising she has worked on herself and wants to try being friends again. We met up, and shortly after got back together. I kept questioning her about the timeline of the guy she started seeing immediately after we broke up, because I believed she was seeing him before. She kept changing the story and I kept pestering her about it. We had a very emotionally heavy month of us being back together, with good times and bad times, but she started pushing me away after a party that she went too. That whole day i was anxious, felt like maybe she had met someone new. Then 3 days later she texts me saying we should just be friends. What's really going on in her head? Did she really care about me? Or was she just seeking comfort and using me during that time. Did she meet someone new? Or we just done now?