Hi Jen!
I, too, am a stepmom, and have been for 14 years. These are some of the most difficult situations that "we" stepmoms can be in....
To give you a quick understanding of my experience, my stepkids came into my life when they were 8 and 10. They are now 22 and 24, so I've been through all the teen stuff and COMPLETELY understand and know EXACTLY how frustrated you are!
The best thing that YOU and your husband can do for your stepson, is to be consistent in your own home. You have to try to "focus' on NOT being upset with the EX. It's very hard, I know, but in the end....by being upset with her....you are hurting your stepson's feelings.
Your responses to your stepson are simple.....you tell him that you love him, and the rules in your home are un-negotiable for reasons for his safety and guidance through the most difficult ages in his life.
You cannot do anything about his mom's house and her rules. And, yes, mistakes will happen that YOU can see coming A MILE AWAY! But...it's her choice, not yours. Your choices are made within your home.
Oh boy, I can tell you stories about my experiences, but I won't take up the space right now. Just know, that after ALOT of practice....it's in the best interest of your stepson to keep your "thoughts and frustrations" about his mom to yourself (or between you and your husband). Always, no matter what, be positive about her....somehow.
I promise.....it comes back to you in 10 FOLD!!!! My stepkids put me almost first when it comes to the most beautiful accomplishments in their lives now. They also come to me with their most troubled issues......nobody else, just me. They've learned they can tell me anything and I will never be negative, only honest and always looking out for their best interest.
It takes awhile, but will last forever. Don't worry, when your stepson turns 20 then the problems will start to "taper off"....hope you can wait that long :o) For now, be the one person in is life that is always positive and "there for him". He is sure lucky to have you!
Good Luck!
:o) N.