How can i end a 25 yr marriage?

it will be 25 yrs. in Sept, he works out of the country, i have to care for our autistic son alone, he is 24 now and wants to drink alittle -normal for his age, his father blames me but he is never home! and he had an affair last year in kuwait, i feel so abandonded, 5 yrs now, our son is uffering too, all i ever wanted was our little family together. what do i do? my health isn't good.