I'm telling my mom the reason I'm getting out of the house is for my own mental health.
Is that the real reason you're leaving?
She's always nagging at me, putting me down and telling me I'm not worthy of being her son.
Getting away from a toxic situation/person is a good thing. You need to make sure your own health gets priority.
But I don't want to hear it and be lectured by someone who I'm always doing things for.
If you are in any relationship that makes you feel bad about yourself the best thing to do is leave the situation. Unless she would be interested in going to family counseling so you can both learn how to communicate in a healthy way.