gf talks to someone she used to hookup with

My gf and have been dating for <7 months. I love her. There’s a lot we’ve in common. We’ve also built a lot of history / memories in this timeframe. She’s been transparent with me about her past, including her past relationships, including hookups. One of the guys she hooked up keeps popping up from calls to text - invitations to parties and games. I trust her and I believe I’m overall a secure person. But for the first time I’m starting to question this whole thing she has with this guy. Yes she says this is long past and they are now just friends but it feels like there are some boundaries that I believe are being crossed. The guy is evidently, I think, not acknowledging my presence in this relationship. My gf is also not stopping that line of communication.

I have talked about this - at least 3 times in those 7 months. And we are at an impasse. I don’t want to control her life in anyway. All I seek is respect - from both parties. What advice if any would you guys give me here? As this continues to unfold, I imagine it’s easier for me to walkaway. We keep it all amicable and wish each other the best