My man constantly talks about his exes.

I've been dating this amazing man for 3+ months now. He went on lots of trips around the world with his ex. Yesterday, we were hanging out and he started showing me pictures of him traveling around the world. Most of the pictures had his ex in them. Am I tripping? I felt weird about it. Why is he holding on to this pictures? They broke up around 2 years now and he dated a couple women before me.