Apart from what the pp's have mentioned there is one thing I would like to add. Is there not still Paternity Leave allowed that he could take? It could be exactly what he needs (in many ways) and would definately help you out as well.
It might be just what is needed for him to not only bond more with his child and be more understanding but this way he still has money coming in on a regular basis than it sounds like he has been? I will also give you the chance to work more and perhaps have some better opportunities professionally (by the sounds of it) so when you are able / ready to go back to work on a more reg./fulltime basis the options (or current Mgmt. position) could be there waiting?
Yes, he does sound frustrated but not just about the usual things surrounding a young family and trying to support them. Construction is up/down depending on what field he is specializing in and even them it's not reliable? this way he has a regular cheque and gets to spend some time with his kids he wouldn't normally be able to do?
Not sure if this would work for you guys but thought I'd mention it?