Man that's pretty shitty how your mom emotionally manipulated you like that. Everyone's line will be different but you do have to draw the line somewhere when an action becomes unforgivable. If you can forgive someone, you should if you want to but if you just don't want to forgive someone's actions then keeping that person around is just going to build more and more resentment over time.

Resenting the people in your life doesn't seem like it will make you very happy at least that's how I see it.