I'm assuming you are a man, forgive me if I am wrong. If your post was written from the view of an SM "I have to make amends for my perceived wrongdoings and shortcomings before my needs are addressed", I would advise you to immediately go home to your mother/sister/best friend and file for divorce. But first find a really, really good therapist to help you find your (girl) cajones and stand up for yourself.  Being able to admit your faults through self reflection is an admirable trait. I applaud your willingness to continuously improve yourself as a human and as a spouse. I wonder, though, where your assessment comes from. Is it truly from thoughtful introspection or is it gleaned from abuse handed to you by an uncaring spouse? You seem unnecessarily harsh on yourself. 

Yoy deserve happiness. You deserve to be with a partner that respects you and builds you up. You have the right to make decisions in the home you help pay for. 

Edit- sorry.."she has decided she won't divorce me". Too bad. Sounds like she needs to go. 

My mother routinely went through every single drawer, pocket, and crevice of her kids' things. In fact, she found weed in the pocket of a friend of my brother when they were in high school. She flushed it, went back to bed and laid there laughing at the sound of ensuing panic. I don't condone this. It makes for screwed up, insecure kids.

But I have to tell you...I think the ladies pulled one over on you. Are you fucking kidding me that she made you confess and apologize to your SD that you...snooped? OK, that ain't right. Unless you were perving through SD's underwear, this "MAJOR" infraction should have been kept between you two adults. Making you apologize is handing power over to SD that probably isn't helping the imbalance in your marriage (although you don't really say that it's SD causing the troubles in your marriage). The fact that you admitted what you did to your wife should make her more willing to forgive you, not less -- an encouragement for you to continue doing the right thing by being honest.

I think you guys need a real-time referee. I might be wrong, but it sort of sounds like you're willing to take responsibility for what you do wrong, and she's perfectly happy to heap the whole mess on your lap. She got a little taste of your "weakness" when you did something a little wrong, admitted it, and apologized for it, so now the power has shifted to her and she's not willing to let it go. I don't think this is unusual. A good therapist will set her straight. A good therapist will probably also give you shit for smoking too much weed, though, so be prepared.

Please, stop beating yourself up for VIOLATING a 16-year-old's privacy!!!!!!! What if you had found a syringe and H in her stuff? Or stolen property? Or nude photos a 50-year-old perv has been sending to her? Frankly, more parents should probably dig through their kids' stuff. The key is not to use anything minor against them and not to admit it -- only raise what you found if it's dangerous or illegal. Nothing wrong with having information as long as you don't improperly use it.

Go to therpay -- you need someone to give you a realistic perspective on what share of this is yours and what isn't.

I used to have respect for my SD's privacy.  Talk about a role reversal.  Turns out, she was going through my stuff, vandalizing things, stealing things, snooping.  It went on for a long time before I was sure.  Then it was on like Donkey Kong.  Now my stuff is locked up and I go through HER room, remove contaband whenever I want, and I make it obvious.  I hope she enjoys the feeling.  It's MY effing house, I am The Adult, and she is The Child.  Parents have a right, and I'd go so far as to say a duty, to snoop on their teenagers.  And there is no reason they need to know unless you want them to.

I don't snoopo through my kids' rooms, but there has always been the threat of it.

It's my home. My rooms. My furniture. My stuff.

If the cops show up, and find drugs in THEIR STUFF, it's still MY HOME, and *I* am liable, which means THEIR lifestyle is at risk.

I trust that my kids know better than to risk their own lifestyle... besides, they'd tattle on each other. lol

I think marblefawn is on to something. I think it's about power. Your DW decided not to divorce you. Well, ducky. Have you decided not to divorce HER? Or are you expected to be grateful and grovel for the next few weeks/months as you so gratitude for her decision and remorse for your supposed terrible actions?

Take your power back. You did something (that I don't think is so awful) and apologized. Time to move on. No reason you have to delay working on whatever issues you two have as a couple while you prove whatever it is you're supposed to prove. She's treating you like a child, and you are not a child. You are a partner. Expect to be treated like one, and if she will not do that, then that is the biggest issue of all.

Counseling. For you individually, and for the two of you as a couple. Do it.

At some point in a toxic relationship we all come to the realization that the situation is a write off.  Though asked, you didn't comment on why you were snooping.  That may provide some extenuating information that can help commenters frame their questions and advice. 

Regardless of the why of  your snooping... I would not tolerate being eternally placed on the sacrificial alter of SParenting martyrdom over your infractions.

It may be time to go and not look back. Particularly if you are a SParent with no BKs and can make a clean break.

I have read your post and comments and I agree with the masses,  perhaps it's time to part ways.  

1. Your house too so "snooping" is not a deal breaker in my opinion. You have a right to know what is happening in YOUR HOME.

2. It appears that there is a LOT of emotional abuse.

3. You deserve to be happy and that should trump all other points made in my response.  

I wish you a lifetime of happiness.  Your honesty is a quality most people do not have.  Try to be a little easier on yourself.  

I recently "snooped" SD 20s room but it was more like ransacked, her room is already a pigsty so not like it mattered and I wanted her to know I was in there.

Several months ago while at work I was robbed, I came home to find medication ( a controlled substance) and my shotgun had been stolen from our locked bedroom, after further investigation SD 20s not working laptop was in our closet and that was missing as well.  SD 20 said she had left the house in the morning with a friend and of course didn't lock the front door (duh), and SD 26 is a known theif and junky so we named her the alleged culprit on the police report.

Fast forward to a couple of weeks ago, SD 20 has a friend that crashes with her at our house, the friend comes to us and asks if we have the powercord to SD 20s laptop because she has replaced the motherboard, I ask SD where she got the laptop and she says she has had it all along, told her that doesn't make sense since it was stolen from our room and we even told her that evening of the robbery that it was stolen and she was hurt, she still maintains that she had it all along and "Doesn't know what to tell us".

So "snooping" was in hopes of finding my shotgun in the blackhole of her room but apparently she has sold or gotten rid of it elseways.

"An important example is that when I have talked about the loneliness, rejection and feelings of disrespect I feel in my identity as a step parent with no kids of my own, she basically minimizes it and tells me I need to stop obsessing about it."

I'm in a similar situation. It's the worst.

I also get very little respect when I mess up to in regards to parenting. My partner expects little of me in regards to co-parenting, really nothing at all yet is not against it when I inject myself into something, but when I step up and do something parental, in a way she disagrees with and I am adamant about, things get really tense. I am made to apologize and change my behavior even when maybe what I was doing was correct and was, in my head, catering to this kid's needs, as I almost took care of my SK15 for the last 3.5 years and know the SK fairly well (I work from home basically). She then asserts that ultimately that she is the mother and I have to deal with that. 

It's tough, super tough, being a step-parent and having a partner that doesn't seem to think it is a big deal that you are a fish out of water all the time in your "family" and that you really do not get the ample amount of understanding you should probably get and that I know I would give if I ever was in their shoes.