I think that leagaly neither can be thrown out. However tension could be so bad that he may well want to go!!
As I said as they are married they will split everything including the house in his name, then provision made for the child.
I would be inclined, if I were him, to leave and contribute maintenance and within the divorce settlement get agreement that the house is to be sold and the proceeds split when the boy reaches 18 or something.
By that time the house may be worth a bit more and you may get something back.
As it is, sell it now and you have no equity into another property for either of you AND you still have to provide accomodation/maintenance for the child so you lose out (in my opinion) more than letting them stay.
If it is a case of "it was my houase before so she can't have it" suck it up and get over it. Provide what you have to and get on with building back whatever you think you have lost.