So I am feeling kinda depressed at the mo

Everythings going fine with the boys and the pregnancy but I am beginning to wonder if I am soon to be a single mum of three.
I have been with chris for 4 and a half years, he had a car accident 3 years ago and has been on crutches ever since because he broke his femur. He is finally getting much stronger and its actually mending so things should be good. But its not, he started to suffer with depression about a year ago, it was a nightmare at times but I always put up with it because I loved him and tried to understand as much as I could.
Thing is, I dont know how much I can handle anymore I thought when his leg started to get better he would slowly start to feel better with himself as he would be able to do more, but its not the case. If anything its worse! He's constantly moody with me and the kids. He shouts at me all of the time and swears and just generally treats me like sh**.
He never goes to bed till about 3 in the morning and then sleeps all day and leaves me to sort out the kids and stuff. when he does get up all he does is just sleep on the chair.
I have spoke about it with him loads of times and usually he says he will try to make things better, and usually they are better for about a month and then it just goes crappy again. We talked the other day and he said he would make an effort to go to bed earlier and get up and stuff but hes done nothing! hes in bed now and its like 3pm. I just feel like a door mat running after him all the time.
I just dont know what to do anymore... I cry about it all the time. My lifes so messed up I dont know how I am supposed to stay with him as I cant see it changing but whats the alterative being a single mum of three young kids....