The most important thing is to have a good relationship with your son, and that he knows you love him no matter what. This way he will not do things that are really bad (drugs/girls) because he won’t want to hurt you.
I went to a zillion Rabbonim and spent a lot of money on therapists. But this is the most important piece of advice I can give you.
Hang on and be very patient, IY”H you will see he will turn himself around. Always keep the door open.