Man, this brings back my shit dude.
First off, what everyone is saying about moving out is true, DO NOT leave your house. If things get bad, the courts will view it as you abandoning your kids, number 1 goal is to keep being a good father and showing that you are trying your best to maintain structure. If you move out and get a job 2 hours away... you are fucked. Honestly, I would say the whole job 2 hours away thing is likely a pipe dream if you want the next 16 years of your life with the kids to function.
I'm going to get blasted for this in here, the same as everyone blasted me for it when I did it myself, but I'm still going to give you my advice. She is done with the marriage, she feels bad, she knows and loves you on some level, but she's checked out and just doesn't want to be the bad guy. She doesn't want to destroy you and wreck everything, and yeah, she knows a divorce will make her life harder, so that's probably in her head somewhere as well. You want to believe it can be fixed and everything can go back to being like it was at the start or something, that its worth saving, but it isn't and you aren't helping by delaying it. It's going to happen at some point.
Here's where my advice comes in, is it possible for you two to put the kids to bed, sit down in your room and go "Hey, we need to talk. We're both trying to make this work, neither of us wants this to be over, but do we really want to keep living like this? You having to feel terrible because you aren't happy, and me worrying I'm not enough or that I can't trust you? Wouldn't it be better if we just stepped back, while we are as rational as we are now, and having a real talk about how we can split as amicably as possible while not trying to hurt each other or cause problems for the kids or anything. I don't want to have the relationship you and your Ex have, we love each other but we just didn't make it, we tried but it isn't working, I'd like to talk about us finding a way to split up and continue being respectful and friendly with each other."
Something like that. Now, you know your wife, if that in any way shape or form seems like a non starter, DO NOT DO IT and go talk to a lawyer like everyone else is saying. For me, its been the best thing I ever did. We can go back to 40 pages of these guys talking about how fucked I'm going to get, and none of that happened. I was on a zoom call last night with my Ex-wife because she bought a new car and wanted to show me and my wife, she's excited and we are all friends. I'm not saying we haven't had issues or disagreements, and I do not think we would be speaking if it wasn't for the kids (would have just been easier to split totally of course). I'm sure it helped that both my Ex and I were products of rough divorces, and we did not want to expose our kids to that. I get that my situation is the 1%, we've gone on vacation with the kids and invited my Ex and her guy, and had a great time. We have a 50/50 schedule for the kids that works for both of us, and both sets of parents are typically totally cool with changing days or whatever. Everything is so EASY. I was married to her for 11 years, very similar to your story (minus the booze and drugs), and I really feel like you guys sound like you are in the same place we were.
I'm just saying, if its an option to work out together, if she is cool about it, it can work out MUCH better for everyone. Especially if you want to stay in your step daughters life, the only way that probably happens is if you can both be grown ups and team players.
I get that this will not work for most people, I get that this could be bad advice. Only he is going to know the situation enough to make that call.
Side note - if that does work out, don't just fuck yourself to appease her. You mentioned her keeping the house and shit... yeah maybe, but figure stuff out. Maybe you guys sell it and split the profits, maybe you keep the house but she gets something else. In my case, I made the proposal that I keep the house, but I also keep all the debt we had accrued (Around $25,000). I told her that she keeps her car that was paid off, and she can have literally anything from the house, furniture, appliances, whatever. She starts her new life debt free and with everything she needs to move into a new place. She agreed to that. She also insisted that she not get child support, but we followed what the laws in AZ said, and she was entitled to it. In your case it will be the other way, she will have to pay you child support (I'm guessing $350ish a month based on the incomes you provided and 50/50 split) and you don't have to just shoot that down because you are wanting to get away. If you can't handle stepping back and calmly going over this stuff, yeah, you are going to have to get help.