In need of relationship advice. LONG

So I have been with my fiancee for 8 years. We have 4 kids, the 4th I'm currently pregnant with. We have had our ups and downs which have been really good and really bad. So I have an issue that has gone on forever the fact is everything is on me, I barely get a break he finds way to get out and does not take any of our children. Being pregnant again I am overwhelmed I won't lie. I want to break down I do not get a break from the children I always have one if not most of the time all of them with me. I can't even take a relaxing shower. I can't keep this up. He finds ways to run to his family but I can't even lay down and him watch the kids. I'm not a stay at home mom either I am a teacher and full time nursing student. I don't want to drive an hr and a half to go see his family all the time he will ditch me too though I feel as if I am a second class citizen I have told him before and he agrees but nothing ever changes. I am at a loss and it is effecting everything I do everything for everyone else and never myself and I want to have a mental break down because I feel I do deserve a little bit. I always give and never once get I know the sacrifices of being a mom but when I have a partner that can help this is why I am upset. It should be 50/50 but it has never once been that way I have delt with this for far too long and I think if it does not I am going to go crazy....