My best friend started dating my ex right after we broke up

Me and my ex were together for over a year and things were really good. We'd literally just gotten back from a trip together a few weeks before he ended it. He sat me down one day and told me he didn't feel the same way anymore, no argument, no buildup, nothing I could point to. I was devastated. My best friend was there for all of it, every conversation, every time I fell apart. She heard everything. Then a couple days ago she told me they'd been talking and that she really liked him. A couple days after the breakup. I can't stop thinking about whether something was already happening before he ended things with me. I have no proof but the timeline doesn't sit right and looking back there were times she was busy when I wanted to hang out and times he seemed off for no reason I could figure out. Maybe I'm reading into it. But I can't shake it. I started thinking about what I actually knew versus what I was filling in with my own fears. The timeline was suspicious but it wasn't proof. I also thought about what I actually wanted. Did I want confirmation that something happened before the breakup or did I want to understand where my best friend's head was at when she made this choice. Those felt like different conversations with different people. I realized that sitting with the suspicion without saying anything was only making it louder. I could keep going back and forth in my head forever or I could actually ask her directly. Not accuse her, just be honest that the timeline was bothering me and that I needed to hear what she had to say about it. Whatever her answer was it would give me something real to work with instead of just the story I'd been building in my head. Talking it through helped me see that I deserved an honest conversation regardless of what the answer was. We agreed the best next step was to go to her directly and tell her that the timeline was something I couldn't ignore and that I needed her to be completely honest with me about when things actually started. Not to blow everything up but because I couldn't move forward with the friendship without knowing. What she said and how she said it would tell me everything I needed to know about where things actually stood.