Okay. You forget about that ex (he's horrible to you! Good job on leaving him), and you start making a plan.
I'm sure you can make it with time and effort. I come from a similar background, and my sister is also the youngest of both of us and she is more dependent than me. But I always tell her "if you want it, you can get it".
Perhaps, staying at parent's place brings comfort, less stress, and less worries about adult life. But at some point, it has to end. You choose how, however.
In your case though, your mom needs to be supportive. You tell her that you're staying at the "family" house until you will successfully get back up. And say it with confidence.
I also suggest you read about "inner critical voice" online. Those who grow up with toxic parents tend to have that voice that makes us believe we aren't worthy of love/good things in life and that we aren't going to "make it". But good news is, with some work, that voice can fade away and your courageous voice and character will rise. Head held high. You can do it @Blackwaterlily