Hi Fly, Sorry to hear about your troubles with your son. I don't really have much advice to offer on the subject as my little ones are still so young. IMO, no don't abandon him, let him know you are there for him. Regardless of what happens, he will know and see later that you were there for him. It's hard because you don't really know what happens when he is going to his mom's or his friends houses. And, like you said, you hear about things after the fact.
I have a close friend who is dealing with similar issues. Her step daughter was acting out and dating a boyfriend who has into drugs and getting into trouble. What she ended up doing was sort of forming an alliance with the step daughter's mother. They worked together as a team to help with the situation. For instance, if they thought something fishy was going on or that she wasn't telling the truth they would call each other and together find out what was going on. Hopefully you will be able to work with your wife as a team, after all you should have a common goal of what's best for your son.
Best of luck with everything, -cp
M: 8 yrs T:14 Twins:7 S:5 BD:'NLILWY': Feb/2013 Mar/Apr/May: MC June: "living in limbo" Sept 12: H moves out Oct 20: reconciling Jan-Feb 2014:MC Feb 2014: separating, and H moved out.