All I can say is…pray for him!
On a more practical note…if he insists on staying at his gf’s house, don’t go ballistic, but let him know that if he wants to live like a grown man, he can pay his own bills, solve his own problems, etc.
If you’re helping him financially now, it’s giving approval to his lifestyle. If he waits to live his own life, fine! Once he’s paying his own bills, doing his own laundry (or having his gf do it), living without your help may not seem so attractive. And, the young lady, unless she’s truly special, will not appreciate the extra work involved.
Is he in college. Planning to go? He may not find it easy at will, paying for tuition and living expenses. I’m sure it would take a full-time job, at least!
However, you should never stop praying for him. Here I go, saying a mouthful, after saying I had no advice but to pray! But, I don’t think anyone should be supporting another adult, who has a lifestyle they do not approve of. However, he is your son, and you should pray for him.
Hoping for the best, and God Bless!