here I am another Codie, butting in with my opinion.
I can see where you are coming from with your mom heart hurting for your son, but let's ask a few questions here, and see what we come up with.
How is his move back home going to flow with YOUR life?
How is moving him back home going to help him with his life? (other than saving a few bucks, which I fully understand)
What are the pros and cons of him moving back home?
My thoughts are WAIT.
Don't give an answer now, wait, think, give yourself time to overcome the "mothering Instinct" and see what happens in a week or so.
As for the GF, yeppers you're right, you can lead a horse to water...but....