I'm almost ready to give up on life

A few days ago my husband decided to walk out on our family. He didn't give a reason why and did not even say anything he just left. Our relationship has been pretty rocky because his mood swings are so up and down and because he is extremely insecure, but we haven't been arguing or fighting lately. We had just come back from South Carolina maybe 2 days prior. We slept in the same bed the night before, we had sex the night before, we ate together, he kissed me before he left for work, he even cleaned up downstairs and put away the Christmas tree like I asked him to. I was gone most of the day running errands and when I came home I started folding clothes. I went to put some of his clothes away and noticed that his drawers were empty. At this point he was still at home and he was downstairs cleaning. I asked him where his clothes were and he said in his bag I didn't ask anything else. I just sat quietly and watched as he grabbed his coat, his power drill and a few socks and walked out of the door and to his car. That was the last time that I saw him. It's been 4 days now. I have 3 children and although only 1 of them is biologically his, he is the only father they have ever known. I have been with him since my oldest was 3 months old and she will be 10 this year. My 5 year olds father died 4 months after she was born and my husband and I got back together shortly after and so he is the only father she has ever known as well. on top of all of this the one child that we do have together was diagnosed with cancer a few months ago when she was 9 months old. I had to quit my job to be able to stay home and take care of her and get her back and forth to the hospital and her appointments. So not only did he leave me to raise 3 children alone, he also left me to figure out how to take care of the children, rent and bills without a job. I think the thing that bothers me most about the situation is how he left and didn't say anything. Also how I can't for the life of me understand why he would leave when there were no problems. I keep trying to tell myself everyday not to chase after a man who would walk out on his family for no reason at all. But the other side of me makes me feel like my husband is possibly bipolar and needs help. I really could use a prayer and some words of encouragement or advice. Should I keep trying to make my marriage work and find out what happened or why he left? Or should I just leave it alone and try to figure out how to make life better for my girls?