I don’t think you’re wrong to be upset about this situation, and losing control of your home to teenagers, but I do think that moving into the guest room and leaving your wife, is rash and wrong. There are a couple of ideas I have that can help you feel like you’re more in control and they’ll restore order to your home:
1. Move back into the master bedroom with your wife, apologize for getting upset and recommitment to her and the marriage. Make up with her. The two of you are important and a 10 year marriage is a great accomplishment. Don’t give up.
2. Calmly explain that you’re concerned for your step-daughter’s safety on many levels because she’s having sex with someone you don’t know and she may not know very well, in addition to which, she’s underage. Your wife may not agree with your feelings but it’s important that you calmly articulate them so she hears them. It’s okay to disagree. It’s not okay to disrespect each other.
3. If it’s how you feel, explain that you’re not against your 17 year old step-daughter having a romantic relationship at some point, but not if it involves her having sex in your home, and certainly not as a teenager. This may be seen as conservative and you should acknowledge that and ask for open-mindedness in anyone judging your feelings. Again, stay calm.
4. Explain that anyone creeping in and out of the house is a safety risk, and you don’t want to stunt your step-daughter’s social life, but it’s important that she learn respect for your home, and future college roommates, young adult roommates, future boyfriends and even a spouse — so for now, you do want to put hours on her guests that are reasonable and you do want to know who is in your home and where she is, as long as she’s a minor.
5. Invite the boy and his family to dinner so you can all get to know each other and the sneaking around ends. You may find that his family are allies. You may even find that he is an ally. And many times, teenagers sneak around because they don’t know what else to do. It may seem like they want to sneak and be rebellious, but sometimes they appreciate being told what to do and why — when it doesn’t come off as punitive.
You got upset because you lost control of your home, and getting control back is important, but you have to do it in a calm and rational way, where you and your wife are partners and a united front (even if you disagree with each other), and show boundaries as well as flexibility and a perspective on parenting. I’m guessing your wife told you to stay out of it because things got heated, but the reality is that step-kids do break up marriages in the same ways that in-laws do, so be empathetic and try not to fly off the handle, and reward your wife for being the kind of mother and wife who makes adjustments and listens to you even when she doesn’t want to and would rather not deal with conflict.
Hope that helps!
