This is not recent, it happened a while back but it still pops up in my head every now and then.

I had a plate who was on her way out but we still would see each other about once or twice a week but it was rocky. I find out one time that she couldn't make it because she and an appointment. She had had several doctor's appointments for her son, but something didn't seem right. So the day of I asked which doctor he was going to see today. She said he didn't have an appointment but she didn't want to talk about it. I left it alone and just assumed she was seeing a guy. I soft nexted her and it ended shortly there after. Honestly I was tired of it at the time and when I think of the whole thing it makes me tired, just remembering it. BTW I don't know that it was another guy, it may have been a doctor's appointment for her, but she felt she couldn't tell me so that maked me suspicious.

My question is, how should I have handled this situation?