Husband left wife for another woman?

I have been married for almost 17 years and about 2 yrs ago my husband left me for another woman and now has 2 children with her.We do share a son together that is fifteen yrs old and does go to school at his fathers home we do share custody and i have have custodial custody and he has physical custody.So my question is that after being married all those years and him leaving and having affair am i entitled to alimony?How does child support work if i am on disability?