The situation with your son sucks but it isn't something you can change overnight - especially if you and your wife completely disagree on how to approach it.
Sounds like the bigger problem is your relationship with your wife. And that's 50% your problem.
Have you considered couples counseling? If you want to stay married, have a chance at a fulfilling relationship and ever want to address the issue of supporting a drug addicted adult under your roof, I hope you will suggest it to your wife.
Whoever said put on your own oxygen mask first before attempting to help others put on theirs is right.
Focus on fixing your own problems and your own mental health. Then you'll be in much better shape to confront all those other issues that are affecting your quality of life.
Another thing you might consider is alanon - invite your wife to go with you. But if she won't go, then go with out her.