person A: I had to cancel on my friend tonight. I felt bad when I did too
person B: That happens sometimes. Sometimes life just gets in the way. Heck_comma_ sometimes you just decide you can't physically do a night out_comma_ and that's okay_comma_ too. I'm sure they'd understand no matter what. Maybe you can make it up to them somehow.
person A: I hope I can too
person B: Maybe take a few days to think it over_comma_ and then when the weekend comes_comma_ think of a way to surprise them in order to make it up to them. Or if nothing else_comma_ just be as honest as possible and not try to cover anything up when you need to bail on them. They'll appreciate that the most.