idk what to do.. I feel like I'm not in a relationship with my boyfriend and not happy... but if we…

idk what to do.. I feel like I'm not in a relationship with my boyfriend and not happy... but if we completely break up then he wants 50/50 custody which I completely don't want.. my daughters only 2 months and breastfed and he doesn't take care of his kids...his mom does.. I want full custody and don't wanna be with him.. why can't I ever get what I want?