I feel like I've spent my entire life motivated solely by someone else's anxiety

My (emotionally abusive) mother has spent her entire adult life dealing (poorly) with depression, anxiety, and shitty self-worth. Thanks to her tendency to project and bully, my entire childhood was spent trying to please her and keep her happy. I eventually left home to go to University; I studied Engineering, not because I had any real passion for the subject, but because I was ok at maths/physics at school and engineers always seemed well respected in society (3 guesses who's respect I wanted...). Despite my flimsy motivation, I got a 2:1 with very little effort and went on to do a PhD, where I floundered due to the motivation simply not being there. I now find myself back "home" with my parents, penniless, all willpower spent, bereft of any purpose in life, and full of self-loathing: living my life for that foul woman has done nothing but make me miserable and angry. I can't keep living like this. I think I need to learn to act according to my own reasons, passions, motivations, etc. I just don't know how to start.

I was hoping someone around here might be able to help me find a raison d'être or even just a way of breaking this shitty cycle I'm stuck in, though acknowledgement that someone out there read this rant would go a long way.