Old Boyfriend messages

Is it bad that I’ve gone through my boyfriends old message he had with another girl 1 week before we were seeing each other ? Also my boyfriend don’t tell me anything about himself, like he’s just says idk or just try’s to get out of it. Like I just don’t know how to go about it. And after I read the messages I just get really insecure and expect that he’s just going to leave. Like he made the girl he was talking to cheat on her boyfriend at the time. Like I know it’s random but does anyone understand??