At what point did you realize your marriage was really over?

My husband and I have been having problems for a long time now. It has gotten to the point where we argue every single day. I believe that we have really just been staying together because we have two young children. What made you finally decide to leave, if you did? I feel like I’m pretty much at my breaking point but it breaks my heart knowing that if I leave, my kids won’t have their father in their lives full time.