Hey Pacman,
You are both the same age right? 50?
If that's the case, it could be a few things. It could be MLC. That is the tail end of the age group for MLC, but it is possible.
One thing that you mentioned that caught my eye was perimenopausal..... that is very interesting to me.
It seems a bit late for that also, it should be full-on menopause right about now. That can have very similar behaviors to MLC.
Which one is it? We don't know,
I would ask if she has trauma in her past, specifically teens or younger? I would also ask if she has abandonment issues (did her parents divorce in her youth?). Any history of MLC in her family? Some of these may be known, and some could be unknown. I learned at lot about mine during her MLC and I thought I knew everything about my W. Is she having drastic memory problems? Is her personality "flipping" on the turn of a dime? Any monstering? Shark eyes events? Dressing like a teen. Hanging out with teens (or 20's). Reversion to earlier periods in time? Being stuck on issues from her past? These are indications of MLC. Not everyone gets them all, but they will have a combo of sorts. If you aren't seeing any of these, and she is in the present..... then that could be an indication that this is solely menopause.
R2T is so right, you will find a way to categorize it as time goes on as you see and experience more. It's also almost universal for every LBS to question "is my MLC'er having an MLC or is this something else?". Happens all the time. It's also a question that each LBS comes to answer themselves.
I know you're beating yourself up about the drinking. I wouldn't. You know this wasn't a good thing, you will have to forgive yourself and move on from it. Actually you'll have to face all your shortcomings, deal with them, improve, forgive, and move forward. Can't change the past, just be the best you can, improve and move forward. If she's in MLC, she's going to have to do the same. It's not easy, but it has to be done.
So you think you may have been in MLC yourself? This is also very interesting..... and to me, if this is the case.... it supports her being in MLC (IMO). How long do you think you were in it? What were your behaviors while in it? Withdrawn? Irritable? Angry? Depressed without admitting it? IF these are true...... then you could have been kicked out of it because she was going into it (that's also fairly normal, not typical, but normal). There are a lot of male LBS's who believed they were in something before their W was. That just catches my eye.
April was BD, so you're 5 months in. Not time for her to slow down yet, and contact will only prolong her descent. There is no catching them in their fall Pacman. As much as we want to save them, fix them, help them....... they don't want it. We only make it worse. This isn't about you, it's about her. She isn't dong this to hurt you or your family. She is damaged. She will have to fix herself. Maybe she will, maybe she won't. Time will tell.
Now is the time to work on yourself Pacman. It's going to be ok, no matter what happens, it's going to be ok. You're going to be connecting dots for a long while. Deep breath and let the mind work out all these things and your emotions. Not a time to act on these things, they are going to churn until they are resolved. You will have to master yourself. You'll have to choose how to work on yourself: How to improve. Find the shortcomings, deal with them, wipe them out. If you were in MLC, figure out what put you there, deal with those issues. Now you get to build the best version of you. She'll choose to return later, or not. You may have an influence on her, but can't choose for her.
So much to face in the opening months and 1st year. A tough road, but you'll get thru it. In time this can become a great blessing if you let it. There is much opportunity.
Keep writing, all that energy, emotion and thought needs to be released. Sometimes the only way to work out something is to vent it, and the issues are legion.

Be gentle, go slow, deep breaths. Take care of yourself. Learning how to operate alone is a big step. Detachment is not easy but necessary.
-SS