First Buster, YOU contaminate your marriage and set things up such that affairs can happen, and so did SHE. I am sure she made mistakes too.
Despite the fact that she used the drugs with you, either one of you could have shown the maturity to stop and help the other one to stop...you both were only thinking of yourselves, not hthe harm you were doing to each other or your household.
DRUGS run a household. But you both participated, she CAN criticize you for that, do NOT ignore that.
If you acknowledge that you BOTH made a mistake and you have cleaned up your home she will have more respect for you than if you hide like a child behind some defensive argument that she isn't going to believe.
Accept that drugs harm households, accept that you and she used them and accept equal responsability along with her for bringing them into the household.
Second, you are listening to what she is saying way too much. She is in an affair and is giong to throw crap at you for a while and you are going to need to learn to NOT let it get to you. You are going to have to learn to stand back and respond maturely to what she says.
She's TELLING you how to SAVE your relationship and you arne't listening. When she criticizes you for using drugs, don't defend yourself, accept it and show some maturity. She clearly is upset at the maturity you showed in using them (never mind the fact that she did too), SHE wants a partner who is more mature than that. So, accept the criticism.
"OK, I did and I am sorry. I even cleaned myself because I wasn't proud of it. The drugs are free from our home and they wont' be coming back. I want a healthy home for our family."
THIS is what she's wanting to hear from you...stop defending yourself.
When your wife criticizes you, LISTEN to it and GROW from it. She's handing you all the ammunition you need to become a more desirable spouse for her. Stop defending yourself and don't attack her.
Yes, move back in. Ignore her threats, you have to stop taking what she says at face value and listen to the subtext. You have a 2 year old son, then use that :
"I want a healthy happy home for our son and I intend on being the person to offer that. This is a drug free home and always will be. We have a family to think about and our family comes first and always will."
etc...THIS will show some maturity. Do you think she wants to hear you argue with her or make excuses? She's accusing you of acting like a child and you REACT like a child by defending yourself.
As far as telling your parents that you used drugs, cut her off at the knees and tell them yoruself. Show maturity here. I would be showing as much maturity as possible. This is clearly what she's looking for from the sounds of it.
Somehow this OM has convinced her that he can offer more of that. And no, he's not more mature, he's having an affair. Is it fair? Of course not. That my friend is a life lesson you will be learning all too well in the near future.
Walk the mature road and don't let all this get to you. Your son needs a parent right now and SHE isn't acting like one. If YOU want to impress HER then act like a parent.
Move back in and tell her that her son needs his father. Clean the entire home up so it is more inviting to a child. And show some maturity to her. STOP talking about what you want or how you feel and ACT like a mature adult.
Lastly, expose the affair. Don't meet with this OM in private and try to reason with him, he isn't going to listen to you. Expose the affair as a childish escape that is destructive to your child's home and to yours.
Affairs my friend are a nasty drug as much as cocaine is. She is addicted right now and she isn't going to listen to anything you have to say. You need to expose the affair and be the adult in your home for the next while.
Ignore her threats and tantrums. Do the mature adult thing and show her that you are the mature adult. She will gradually learn that SHE is the child and things should change for the better from there.
Don't react to her behaviour. Do'nt let her fits intimidate you. Do what your family needs. This is YOUR SHOT to be the ADULT in the home.
You BLEW it last time when you brought drugs in and shared them with your wife, NOW you are paying for that. CLEAN UP yourself and aim for a clean home for your family. That is the mature road and the one you will have to walk for some time to come...probably the rest of your life. Get used to it.