So a little backstory. My (47F)girlfriend and (46M)I have been together about 4 years now. We met in late 2019 and got together in 2020. When I first met her there was a female coworker she used to spend a lot of time hanging out with. It didn't bother me and I thought nothing of it. Well I found out later after we got together she was fucking around with this coworker without my knowledge. So she pretty much cheated on me with this coworker. So she stopped hanging around with her and I accept the fact that they work together and that she has to deal with her at work and communicate with her at work. But now she's going to a campsite with other coworkers that she's done for years now but that other coworker will be there.

Am I being an asshole for not wanting her to go because that coworker is going to be there?

Am I overreacting for feeling some type of way that this coworker is going to be there?

Because my girlfriend is acting like I'm overreacting and throwing this way out of proportion and making more of it than it is. I don't know maybe she's right maybe I'm being an asshole. I am kind of a dick sometimes so maybe in this instance I am being an asshole. So I figured I'd ask you guys.