From my point of view (FWIW) it sounds as if you are in a horribly stressful situation, with money and lack of a job, etc - and of course this is heightened because of worry of a new baby on the way.
I think it would be impossible for ANYONE to be coping very well in your situation, either of you I mean, and I think you are both very very unsupported - you obviously have little or no help or break from the kids, and you must be highly stressed and exhausted.
I think your feelings of wanting to escape the relationship are at least as much to do with wanting to escape the situation you are in. And I think because you are 'alone together' and pretty much unsupported, you are bound to take it ALL out on eachother, which puts you as 'enemies' and removes the last area where you could be supported - ie by eachother. It's then a downward spiral, do you know what I mean?
If there was some way that you could have a shift from this position of enemies to facing it together, I'm sure you could save this situation. It's just difficult to get there, I know. When I had some problems with my relationship with DH, I wrote a heartfelt letter to him because it was easier to get it all out and know that it wasn't going to turn into an argument. And it worked, because we inched closer to being 'allies' again rather than heading in our selfish directions. From there we were able to plan calmly to sort out our horrible financial situation - and things are so 100% better, I can't tell you what a difference it makes. That's why I've taken the time to yabber on, because I know that in my case 80% of problems were the situation rather than the relationship - but we had to work on the relationship first, a bit, to make it possible to sort the situation together rather than by splitting.
Phew! hope some of that makes sense. Am thinking of you...