Am I overreacting? GF might have cheated on me at the start of our relationship

Hi all, I (25M) been with my GF for a year and half now, we met in college around covid time but didn’t really hit it off then. But I reached out to her around later 2023. While we were still in the “talking stage” I was away in a different country, I’d often see her partying with her friends etc mostly all women. But there was this guy, call him S, she’d meet once every month or so. I was away for around 3 months before we started dating, and she met this guy around 3-4 times. Because we weren’t really dating she’d tell me much about where they were going etc but usually just that they were having dinner together. S isn’t her one of her ex either as she had broken up with someone recently right before I reached out to her.

Anyways when I got back, we started going out, she would still meet S, every now and then. What I always found strange was, they had no conversation or chat history. It was always something like “hey meet up tomorrow right?” And thats all. They’d agree and go for dinner. A lot of the times the invitation went from my GF, this I found out years later btw. When we were dating I’d try to get to know more about S and what they did etc, but she’d always be very vague, like S is just some dude shes been friends with HS and they just meet every now and then to catch up and S is very busy. S wasn’t dating anybody and Idk if my GF even told him we were dating as everytime I asked her to introduce me to S she’d just say No, as she hasn’t told many friends about me and S isn’t really close. Which I always found weird to begin with. They met up a few more times in the next 6-8 months of us dating. I’d just show her trust and respect her wanting to meet her friend. She’d always be home within a few hrs as well to not add anything to my suspicions. It was around a few months after that, she hadn’t met S at all for months when I started thinking and questioning what had happened, so I asked her aboht this and she said “S has just been busy and out of town”. Fair enough I said

But this went on for another few months, until S randomly texted my GF in summer 2025, nothing suspicious just a simple “hey what’s up”. My GF never replied back to it and that’s when I knew something was definitely wrong here, so I asked her again and she got a bit angry with all my questions, which as her BF I think I deserved to know. She was annoyed but she told me that the last few times they met S had been acting weird, a bit annoying and just trying to get “close”. They never saw each other again but something about this still haunts me, whether what she told me was true or there is definitely more to it …..