Why did he stop in the middle of making out?

Fyi, this is the first guy I'm with. I've just started dating this guy and we have just gotten to the point of kissing and making out, so we are not that close yet. Otherwise I would ask him straight out. This was like our second or third time just laying in bed making out. He is on top of me and it is a good time. All of a sudden he just stops and like rests his head by my neck and after awhile he rolled off me. I don't get why we stopped because I sure didn't want to :(

It might be a really dumb question but I also feel dumb as I have no experience and maybe there is an obvious answer

Why did he stop in the middle of making out?
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