As a guy, lots of guys get like, 2-5 close friends and they are content with that. They don't have time to spend with more than that, why bother with more? Not everyone needs dozens of "friends"

A girlfriend/sexual partner is different. You can make an exception for a sexual partner, they're ideally going to be a friend as well, so you want to be friendly and make sure their interests are somewhat compatible. Generally speaking that bar is a fair bit lower for sexual partners.

But once they tell you it's not going to happen, they're just another potential acquaintance you aren't going to have time for. Being a "normal person" is keeping your friend circle tight and high-quality. Sounds like you were compatible enough to be a sexual partner, but not enough to be an actual close friend, so once partner was off the table that was that.