AITA for wanting to break up with my girlfriend after I found out she still talks to her ex?

So, I (27M) have been in a relationship with my girlfriend, "Lily" (25F), for about a year now. Our relationship has been mostly great—we get along well, have fun together, and genuinely enjoy each other’s company. We’ve had a few minor arguments here and there, but nothing major.

Recently, though, I’ve been feeling uncomfortable with something that I’ve discovered. One of my friends mentioned to me that he saw Lily chatting with her ex on social media. Naturally, I felt uneasy, so I decided to confront her about it.

At first, she seemed taken aback but then admitted that she still talks to him from time to time. She said it was "just catching up" and "nothing serious." She told me they don’t talk about anything personal, just “light” things. She even showed me some of the conversations to prove it wasn’t anything inappropriate.

While I understand that they may have a history and that breaking up with someone doesn't always mean cutting ties completely, it still didn’t sit well with me. I’ve been in relationships before where an ex talking to someone constantly can create tension and insecurity, and I don't want that to happen in this one.

I told her that I was uncomfortable with her still talking to him, and I asked her to stop. She got upset and told me I was being controlling and that I should trust her. She said there’s nothing wrong with being friends with an ex and that it’s normal for people to keep in touch after a breakup. She promised it was nothing serious, but I still don’t feel great about it.

Now, I’m torn. I trust her, but I also feel like there’s a line that’s being crossed here. Am I overreacting? Should I just trust her and let this go, or do I have a right to feel uncomfortable and ask her to stop talking to her ex?

So, AITA for wanting to break up with my girlfriend because she still talks to her ex?