i'm so sorry, chicory, this sounds so painful. i don't know what to say, because i can hear that you do have the answers inside of yourself. but i do want you to know that i'm rooting for you, and for your son as well.
if you are set on following through with allowing him to stay until he secures the job, can you at least leave in the evenings? hang out at a friend's house, a coffee shop, go to a movie or library....to not be around it seems a little more comfort.