Why do I get attached/gain feelings for every man I have sex with?

I always gain some kind of attachment or something when I have sex with a guy. It’s annoying because I want to be single and just have one night stands but then after we have sex I want their attention. Thinking about them with other girls upsets me even though it never upset me before.

Some of these guys I’m not even attracted to THAT much but I still feel that way.

I get over it after a while but even when years go by there’s still a small touch of feelings that will always stay.. not as much as the beginning but i never fully get rid of the feelings. A part of me still cares