Am I being paranoid?

My partner has openly admitted to staying in touch with his long term ex which I have no problem as such with. However, I've got this gut feeling that there's more to it than just the occasional casual chat. I'm going to speak to him later about it face to face and I'm going to ask to see the conversations between them (not ideal I know but I need to put my mind at rest). If he won't show me or has deleted all the messages to me that says he is hiding something more than just asking how she's doing. Am I wrong to think that? Am I overreacting and being paranoid? I've been cheated on and hurt badly in the past so trust issues is something I have with everyone in my life. If he doesn't let me see the conversations or has deleted them I'm immediately going to think there's more to it. If this is the case I think I'd probably end up finishing our relationship 🤔 opinions welcome but please no need to slate me.