Anyone else upset when you're in a bad situation and begin to "coast" again?

I've faced some difficulty with past relationships. My mother has uBPD and threatened me (with ending her life, standing in front of my car, etc.) so I wouldn't leave her in the moment. I believed I had moved on. Turns out, my current partner engages in the same behaviour, with large emotional outbursts and very negative self-talk. This includes talk of breaking up, if I even simply suggest seeing family on my own for a few days.

Now, I'm feeling so trapped and helpless. I was making great strides with assertiveness but now feel like I can't even look people in the eye. I'll tell friends about the situation and they all say that it needs to end one way or another, but I just can't. I feel like I can change, like I'm not considering the ways I've been hurtful to them, like I'm not being patient enough to wade through this difficult time they're experiencing until they learn that such behaviour is wrong.

What is something you might do to help break this feeling of coasting? Especially when taking action invites such dire consequences.