He's not seriously looking for a job. Either pay the $800 and get him out, or move out yourself. This situation will not improve.

Your son is not the main factor in any of this. Don't make this about your son. End the relationship because it is beyond ridiculous to remain in it.

I know it can feel awful to sever ties with someone, fearing the person will become homeless. (I've been there and done that. It's like emotional blackmail.)

Your son can just ignore your boyfriend. Forget the apologies. Ask yourself why you are with this guy? What would the $800 pay for.