Trust him when he says he’ll do something about it once his mom has the money.

If you can, offer him money already to see if he’s really serious or not.

He’s still a boy, as Mark said.

After you wait patiently or give him the money sooner, you’ll have one of the 2 situations: either he won’t do something about it, or he will do. For the first one, it will be up to you if you continue the relationship and be always frustrated and causing fights that will lead to a breakup eventually, or break up with him from the start.