Uncomfortable with Sex

So I made a post about this a couple days ago. But I just recently had sex. As in yesterday with my SO. And I told him I didn't feel like having sex anymore. He was fine with it but was wondering why. And the truth is, I'm scared of getting too close to him. I'm scared that we'll have sex a lot and I'll get so attached to him. But if he ever leaves, I'll be destroyed. So what the f-word am I supposed to do.