I'm heart broken

I'm caught between wanting to be strong and not let him see me cry, but a part of me wants to openly mourn the fact that my children's father and I are probably over for good. I've been with him on and off from 2010-2013 and then we were going strong from 2013-now. Built a family and honest thought I'd end up marrying him. He thinks I am the one who made the relationship difficult and I feel like if I cry then I'm taking the blame or practically begging him to stay and I don't want that. It just hurts to think you mean so much to someone and then they just walk away.