Is the house yours or your husband's or both of yours?

That makes a difference

If the house is yours say "No". If your hu*****and insists ask him to move out and live with his son. You have to be firm.

If the house is his you can not say no

If the house is both of yours ask your hu*****and to pay 70% of the expenses of the house after his son moves in.

You have a decent job but there is no reason for you to cover any one else' expenses. This ex wife apparently has problems too. She can no longer collect child support so she asked her son to move in with you guys. It is too bad for the son. A 26 year old still live with parents? Good luck to his career and even getting a girlfriend.

I think you are very very nice. If it were me, not only I wouldnt allow anyone else move in but also I will let the guy pay majority of the expenses. I divorced with no kid and live with my boyfriend right now. We bought the house together he paid 90% of downpayment I paid 10%. He also covers mortgage and pretty much all the daily expenses as I have my own mortgage to pay off as well. He only makes $10K more than I do per year. If you set things 50% 50% it is hard to change but you need to swing it back somehow.

Or maybe if you have one child together things would change. If not, take good care of your daughter. You only have one kid but there are lots of men around.