Why do I have to worry so much?

I am always over thinking and worrying about everything. If my boyfriend talks a little differently or doesn’t answer my texts, I think that he is mad and wants to break up with me. He constantly tells me how much I mean to him and that he doesn’t know what he would do without me, yet I’m always worried that he’s lying or has an ulterior motive. I keep starting fights when he’s not doing anything wrong and he’s always telling me I need to stop worrying so much but I can’t, its driving us apart.
I worry about really dumb things, for example; next week I am working across town all day so theoretically I could go to his house after and sleep over, but then I would have to catch a bus to work from his house early and I don’t want to shower there. If I don’t see him I will miss him terribly… Now I can recognize how dumb it is to worry about something so small, but I can’t help it.
Or in September when school starts, we can’t have sleepovers on school nights… What if I work on the weekend?
I feel like I have made him too important but there’s not much I can do about it now because both of us feel like we need each other.
I want to be with him constantly but I don’t want to seem clingy or for him to get tired of me and I have a seriously unhealthy obsession with the idea of him leaving me, like I panic every time I think about it.. As you can see I have a lot of irrational fears, and I havent found myself able to talk to a therapist about it without withholding things or flat out lying, I am making myself sick how do I just chill?!