Girlfriend persistent about hanging with ex. AIO?

TL;DR: girlfriend has made several attempts throughout our relationship to hang out with her short-term relationship ex. Should I worry? Am I overreacting?

Long story long, my girlfriend of 3 years has an ex that she previously only referred to as a friend. We all have mutual friends, so one of them let me know they had a thing at one point. I brought this up to her and she almost laughed it off saying “that lasted for like three weeks. We hooked up once and it almost kinda ruined it, so we just stayed friends like before”. I believe this was before we even met, and we’ve known each other for 4 years now. I know they’ve talked pretty consistently since whatever it was ended. He was trying to help her get a job in his city when her and I reconnected (it would’ve been her dream job, and it’s a big city, so I can’t assume she was moving for him). Early on in our relationship, she let me know that he’d been acting weird and distant and she was trying to save their friendship. They eventually did, and she let me know that while they wouldn’t be hanging out anytime soon, they seemed to have corrected the course. Since then, she’s tried to meet up with him several times while visiting other friends in his city (she does let me know each time, albeit after asking him. I know there’s one occasion where she didn’t give me a heads up and was just trying to see him even for ten minutes). It’s fallen through every time and seems to get her a little down. Most recently, she let me know she invited him out for a drink when he’s in town for his birthday. I half-jokingly said “…like a date?” And she reassured me that I would also be invited. I almost feel like my invite was added based on my reaction, as the original proposal was pretty vague.

There are more details, but that’s the gist. Ultimately, she seems quite fixated on a chance to see him. Again, I know they were also friends in college, so I get that they have that history. I just worry that she might be hung up on him and I’m just the backup. Me and this guy are pretty similar in terms of hobbies and such, but he is objectively better at them lol. They also work in the same field, so I get they have a lot in common even just as friends. Am I overreacting? Should I talk to her about it? I’m worried that if I just ask point blank about lingering feelings, I