What boundaries to set for my 29 yr old alcoholic son?

My son lives at his gf's house Sun to Fri. She enables his drinking. She does not really drink. She has 2 kids. He stays at my house on Fri and Sat nights. I don't allow the drinking. He has snuck it in. He also has had seizures from withdrawl at my house since I don't let him drink. Ended up in the ER. His siblings will no longer talk to him until he gets sober. He's not invited to family get togethers. I don't give him money. I don't buy very much for him. He is not abusive to me. (Except for the constant worry). I feel if I give him tough love and cut ties with him, his gf will only continue to enable him. He may die and I will have not spent time with him. I'm just not sure how to move forward.