It's difficult.
If you decide to go ahead with the separation - Will your son have regularly scheduled time with his dad? I found it important to stick to a regular schedule and I often assured my son that he would have special time with his dad during these times. It worked out very well and in fact I think my son really enjoyed the focused time with his dad and got along just fine when he wasn't here.
I've seen some books on controlled separation which I think progresses you through a separation and makes it goal-oriented, having the separation be a way to improve your marriage. Never did try that as AH was still drinking and then had too much on his plate with recovery but it seemed interesting.
Keep focusing on you. Letting go and letting God helps me a lot, especially with financial worries, although I did put aside some $ in an account for myself, when I was working and that gives me a bit more comfort. Maybe you can do same, it seems like you are pretty financially savvy, couldn't you figure out a budgeted way to put some $ aside in account just for you?