history: I canceled on my friend tonight and felt bad. I was just tired I had to cancel on my friend tonight. I felt bad when I did too 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.
current: I hope I can too
next: Maybe take a few days to think it over, and then when the weekend comes, think of a way to surprise them in order to make it up to them. Or if nothing else, 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.