Well, you started in the right place...with yourself.
Let me ask you something: If she never returns to the marriage are you going to go back to being dependent on drugs or are you going to be changed4good? Hopefully the answer is that you are going forward with the new clean you regardless of what happens. Continue to look for other areas where you can make improvements...for YOU.
Your wife would have probably noticed, and approved, except that she's cheating on you. What are you going to do about that? Just being the stay at home husband that facilitates the cheating? Who provides financially? Whose money is being spent to finance these cheating trips? You need to protect yourself financially. You need to protect yourself emotionally. You need to draw some boundaries. Move half the joint money into your own account and then start putting all of your pay into just your account. Cancel any joint credit cards and just get one in your name.
I know you screwed up, but that doesn't give her a free pass to whatever she wants to do with this OM. You can stand up for yourself despite how you feel about your messing up. Nobody wants a guy that sits in the wings waiting for the fling to pass so he can have seconds.
Think as though she's serious about it ending. Whose going to have custody of the kids. Whose keeping the house (or are you renting?)? I know these are unsavory to think about, but she needs to see you not only changed, but also strong and independent. When she comes back, you need to be ready to confront her on this, have boundaries considered, and have the financial stuff figured out. I would do it ASAP. Call tonight about the credit cards if you have any. Get to the bank tomorrow and open your own account. She needs to see you're serious.
You cannot be lonely if you like the person you're alone with. Dr. Wayne Dyer