Unlike child support, spousal support is often very difficult (if not impossible) to modify after the divorce is final, so getting it right the first time is a must!
Don't assume you will have to pay SS. Prior to my divorce I made $135K and he made $22K. I stayed in the home with the kids, paid the mortgage and all other bills and had an order of protection against him (He was and still is a mentally ill drug addict.) I never paid him temp support and he agreed to no SS after the divorce (he was desperate for the equity from the home out of the settlement.)
If your STBX has a college education but makes so much less, they could have his income imputed higher. Has he ever made more? Is he purposely keeping his income lower?
The other posters are correct in that you could go to your home today, force your way in and start living there again and there isn't a thing he could do about it. However you really should have filed for divorce by now. That needs to happen ASAP.