Those surgeries/illness could very well be the spring board that led into the crisis...
I would do a legal sep. if I were you...in fact that is what I did and it saved my butt from financial ruin...especially if you live in a community property state...
You could check with your local court house to see if they offer assistance for filling out and filing the paper work needed...this is what I did and it saved me tons of money...they even provided me with a financial waiver so I didn't have to pay the $300+ to file!...I took the form for the agreement and retyped it the way I wanted it...it was basically a fill-in-the-blanks form anyway...the attorney that looked it over after I was done said that I had done a great job...I had spelled out the visitation arrangement, financial assistance, childcare if it was needed, medical and financial responsibility and because H was so crazy I even had a clause in there for my son's protection if anything should happen to me that my custody of him would transfer to his sisters and everything with his dad would remain the same...H would not assume full custody at any point!
LS is not the end...it isn't a D...but it is a legally binding agreement that can make things run smoother...people tend to forget what they say so having it in writing makes it fair for all involved...if they signed it and agreed to it...then they hold to it...
Ironic...I had 2 kidney stones too...worse pain I have ever physically felt in my life...and the S from H...the worst emotional pain I ever felt...what a period in my life!