Whether or not he is at fault is a moot point. You can't change his behavior. Focusing on his fault is not going to get you the support you need.
You can (and must) make sure that you will be OK even if he isn't there for you! However unpleasant it sounds to ask for help, you (through no fault of your own) have a disease that requires you to get help at times. Your disorder is no less worthy of attention and care than your sister's epilepsy or your father's health conditions. You didn't choose this any more than they did. And it isn't any less severe than their health problems.
Your family and his family is not your only possible support!
My sister is deeply religious, in her church when someone has a baby, the women of the church come together and cook for the new family for an entire month. It was such a kind thing for them to do for her - her husband is military and they were recently stationed 2,000 miles from any family or friends.
Without family, she asked for help and got it in a big way.
I have a client with severe mental health problems. Her pastor and pdoc helped her find an older coupel that have "adopted" her, they call and check on her when times get tough. They even drive her to her therapy appointments when it is not safe for her to drive.
These are 2 examples of people who had no support that got out there and MADE IT HAPPEN. They proactively got what they needed.
I had to do it too. I was divorced after months of post-partum bp cycling. MY XDH kicked me out with my son, my dog, my car and the clothes on our backs. My parents let me live with them (NOT a fun situation) while I struggled to find work for several months. I joined a church group where I got support, wonderful lasting friendships, help finding a job. The church helped me financially, people helped me renovate my house when I finally could move away from my parents. These random strangers became closer than my family.
I moved away, and I am slowly doing it again. I can't allow my fiance to be my only support. It is not fair to him! So I'm making friends with neighbors, the lady at the post office, the librarian, gradually forging relationships and friendships that will be my future support system.
Supprt systems don't just happen, they are built. If you are willing to try, I have some ideas for starting to build a support system so that you are not alone (regardless of what your husband chooses to do).
Borderline Personality Disorder
Post Traumatic Stress Disorder
"It's never too late to become what you might have been."