The sex part isn't that bad, I tend to just reuse past lovers or pleasure myself with sex toys lol
I think the worst part is just being lonely period, not really just the nights, I don't live alone so I don't get to sleep with someone all night anyways. I think being lonely and not feeling like you have someone to talk to is the worst. Being able to call someone to even just talk about your dad and being able to talk about anything and everything is really what makes a relationship so great. When you break up you might try to still be friends but the connection will never be the same.