Advise needed

So my bf and i have been together since 2013 and we have been through ALOT but we are still trying to make things work because we both know we want to be together in the long run. Relationship wise we do fine when we are communicating and not yelling but for him our biggest issue is sex. I literlly can go 6 months or more and not bit more think about having sex and he thinks im simply not attracted to him and i dont know what to do!!!! He just dont understand after working 8 hrs, going to school on tue and thrsdays after work til 7 and coming home to tend to 5 kids cooking cleaning baths hair and everyones homework im tired. Now he cooks time to time and helps with kids so i can focus on homework if im behind when needed but im still to tired or just not even thinking about it. Then its like we not married and that eats at me to on a religious level so im just stuck!!!! Any thoughts ladies???