Why is he wanting to talk about sexual topics when he has a girlfriend?

I have a friend who is now in a relationship but he's gone a bit strange, (he did this one other time but in slightly different manner). He suddenly wants to ask me inappropriate sexual questions or share sexual related stories from his day (e. g things he hears at work etc) to me which is weird. Why is he acting this way? 😔
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Sorry, I passed out 🤣 Just an update: I called him out once more last night asking him how his girlfriend would feel if she knew he was asking me such questions. At first he did the whole downplaying it, but I repeated myself which he seemed to be unhappy with because he blocked me. I feel for his partner because it seems he doesn't realise or want to realise his behaviours are inappropriate.
Why is he wanting to talk about sexual topics when he has a girlfriend?
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