Why is it so hard to leave when you know how bad it is?

I KNOW I can't keep living like this. Today he got mad out of nowhere again and he is just so vicious with his voice and words, the stuff he says gets scarier everytime.

He hates my family and said how he would make my BIL go missing and my mom too. Yelling "I get real mad REAL mad" and I don't remember exactly what he said because I just started disassociate but I'm pretty sure he was insinuating that he's getting to the point he can't control his anger and that it might get physical. he apologized after but I'm so scared. I NEED to leave.

our 4 month old son was in the bedroom while he screamed just SO loud at me. So loud and I try not to look at him when he's like that but I caught a glimpse of his eyes and there was so much hatred.

then lovebombs me like nothing happened.

I'm getting so scared of him. I've been working on a safety plan to leave but it's so hard. why is it so hard when I know how abusive and awful this relationship is