Guy's Behavior

Why does he keep telling me about other girls he slept with?

Two years ago I had a fling with a guy who was three years younger than me. I could tell he was not much experienced sexwise by some little details, but it was just amazing anyways and I often told him. I moved to another city, we kept in touch, became good friends in spite of the distance, and bumped into each other again recently after one and a half years as I moved back. Things catched up where they had left, and work well (we are not in a relationship, too soon). But there is something that pisses me off terribly. The first time I went over to his place, and he could foresee I would, given our precedents, there were things laying around that some girl left there and he didn’t clean up. He keeps telling me things like “flatmate x never brings home girls, flatmate y and I do” or “that girl I slept with said this and that” or even, he tells me his “crazy sex things I did when I was drunk” stories. I told him it upsets me, his explanation: we are close friends and therefore he thinks he can tell me everything. My interpretation: a. He doesn’t want things to become serious and he is letting me know I’m just one out of many, b. He is insecure and thinks that telling me these things will make him look cooler. Why do you think he is doing that?
Why does he keep telling me about other girls he slept with?
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