NewRoad, i'm going through something very similar but I don't have children and appreciate that makes things even harder. There are lots of people on this forum though who do have children and going through same thing so sure they will be along soon.
I have been with my ABF for nearly six years and were planning marriage and children so I thought we would be together for life. I can relate to the guilt and anxiety - my XABF has had several job issues that have made me stay. He now has a very stressful job that doesn't pay great and I worry about his finances but I have only just realised that I am not responsible for him and that he is responsible for himself. That took ages to sink in as I thought it was my role as a caring partner to help him. You seem quite far along in understanding what you can do, and also importantly what you want to do. I didn't want to be someone's helper and you should'nt have to be his.
If you can, go to a meeting for affected others such as Al Anon - I am going to counselling and it is really helping. And this forum has been invaluable for support and advice so keep coming back.