can't stop thinking about my gf ex bf

I'm currently back in a relationship with someone I previously dated for 3 years. We were separated for 3 years, during which she was in a relationship with someone else. Since getting back together, I've noticed some signs that her ex might still be on her mind, such as seeing his name in her recent Instagram searches.

This has made me feel uneasy, and I have become obsessed with him. She is unaware that I know about this ex.

Our relationship is generally really good, and we've been working on rebuilding trust and communication after our time apart. However, I think I'm going to make myself ill over these thoughts.

Should I approach a conversation with her about this? What are some strategies or questions I can use to navigate this sensitive topic and gain clarity on where she stands emotionally?

Would love to hear about how people dealt with similar situations.