M26 & F23.

We've been together 2.5 years. Long story short, she hated working at this place but always got along well with the boss (M30ish).

The last thing I want to be is one of those asshole boyfriends who doesn't "allow" male friends, I'm worried that if I bring this up, that is how she'll interpret it. For the record I couldn't care less of the gender of her friends, just this one particular person.

She left this job about 5 months ago, but still keeps in touch with him, and will often bring him up in conversation even when I am visibly bothered by it. They went to a concert together while she was employed by this guy, it was a metal concert (im not really into that kind of music). I didn't mind because he's a huge dude and I figured she'd at least be safe with him and I have no reason not to trust her.

My concerns started arising well after she had left the job, she was still bringing him up in conversation, and then mentioned that this band was coming to our area and since I wasn't super keen, she'd probably go with him. This is where I showed a moment of weakness and scrolled their messages while she was asleep. He outright stated that he didn't give a fuck how it made me feel, they would be going together, and she seemed on board with that sentiment.

I'm not trying to pin anything on my girl, she's done nothing. I just don't trust this guy. He made the occasional sexually charged comment in their messages which my girl seemed to brush off/ignore completely. That paired with the blatant disregard of my feelings which, from his perspective, is the boyfriend of this girl he's talking to. Idk man.

Are my feelings validated or am I overreacting? How do I best approach this?