I've been through a marriage break up, fortunately it didn't involve kids. I believed the marriage was for life, and I prayed to God for him to save the marriage. It ended anyway.
Looking back at that, it was the best thing that could have happened, although it didn't feel like it at the time. I thought I'd never feel better, but I do now.
God had the bigger picture, and was right there with me when I was hurting, although I couldn't see it at the time. He knew he had bigger and better things for me.
So now when things get tough and my emotions overwhelm me, I remind myself of that, and it helps, sometimes only a bit, but it helps. Something I also do, when I can, is try to remove from me the focus of my feelings, and focus on Jesus instead. That gives me respite at least. But in the words of Peter "Lord, where would we go? You have the message of eternal life".
Hang in there, and use any help God sends to get you through this.