Damned if you do, damned if you don't.
Do this and you will hate yourself longer because you can't say no and the guilt will kill you. Plus, your self respect has been through enough dontcha think?
Do that and you will hate yourself because you dislike not pleasing people but you'll feel better in the long run.
Either way you'll feel bad BUT… the other will help you in the long run.
You deserve better. You've been saying it for years and you know it's true. It's going to be okay.
It's okay to say no.