How do you break up with a person?

It's super hard for me to do for several reasons. The biggest one being that I feel like he's super in love with me and wants to eventually marry me but I'm not sure if I want that anymore.

After last night, I'm not sure if I want to be with him at all. I feel we are somewhat incompatible physically and our beliefs are totally different.

I've tried to see if this would work because we don't live together but everytime we do get together I feel there is something missing. I would hate to move in with him and things get progressively worse.

Maybe I'm just being paranoid. Maybe things are fine and I'm just freaking out over a small detail. But a huge part of me thinks that I'm not. That it's a sign.
How do you break up with a person?
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