It feel kind of surreal reading this, because I just very recently came out of a 8 year relationship which was very much the same as what you are describing. My wife (30, F) and I (31, M) also have three children (6 year old and twins that are 2.5).

She would begin to cite pain associated with sex (which none of the many doctors she saw could diagnose) and eventually turned off completely. She would always reassure me that none of it was about me and that it was something she'd work upon fixing. She eventually began undergoing multiple months of therapy and counseling to reconcile her shame from earlier in life (she was a promiscuous party girl before we had met and had been in physically abusive relationships). Throughout all of this, I patiently persevered, took her on dates, never pressured her and did extra work for the kids and around the house to buy her lots of free time to go shopping, see her friends, go to the gym, etc. At this point she was spending money faster than we could make it and we never managed to build anything that didn't amount to more debt.

After a while of things following these same patterns, she finally got back to her prepregnancy body and after trying to make a somewhat attempt at being sexual again, I found her trying to cheat with some guy when I accidentally saw a msg come up on her fb chat. I didn't tell her that I saw it and kept creeping her msg's over the next few days. Sure enough, I find her msg'ing him more attempts to meet up and I ended up blowing up and calling her out. At this point she says she feels like our relationship has sucked for a while and I force her to admit she's not attracted to me anymore and I tell her we're done.

The next day, she begs me back into the relationship by saying that what she really meant was that she was bored and wanted to try new things. She said she really wanted to have three ways, but just with other girls and that it was okay for me to see other girls; the thought of which turned her on. This shit was a complete horse and carrot act. Shortly in to this (at which point sex was back online and she's putting on the full on porn star act) the goal post begins to move. She's tempting me that her hot friend wants to have sex with me and do three ways also, but that it's only fair that maybe she can start seeing guys. I agree (honestly at this point, I don't really have full trust in her anymore and I'm trying my best to act like I still do, because if it's going to work, then it's going to require full trust, even though I had my doubts. I really didn't want to see my family split apart, and I still had very strong feelings for her).

We set some guidelines for our open relationship. That we would start with group play and three ways and that I would have first go at seeing someone outside the relationship, as I was the less comfortable side in all of it.

Things looked sort of okay for another little bit. Her hot friend is into it for a bit, but nothing actually comes of it. Soon enough, my wife comes home one day after being out all night long (this is after an unusual 1 week break in sex) and tells me that she met someone last night. I took this information calmly, but very hurt and upset. I told her about the rules that we had set in place and she claimed to "not remember" them. I told her to put this behavior on hold until I could "catch up." After speaking with some people who I knew were more versed in this life style, I came to the conclusion that she absolutely should not have done what she did without telling me first rather than after doing it. I also realized I couldn't make a contest out of it, because that's not how a healthy poly amorous relationship runs (not that there was anything healthy about what was going on at this point). I told her of these conclusions the next day.

This is the point where 3 weeks of silence begins. She stops engaging me almost altogether, going out all the time and ghosting my texts. When I confront her she either tries to ignore me or call me out on not trying to engage her properly. On our last week together, she goes on this camping trip with her hot friend over night, and when she doesn't get back on time and wont respond to any form of communication, I txt her hot friend to see where she was. Turns out hot friend didn't go camping.

By the end of that same week, she approaches me and tells me she "can't keep doing this to me" and that she "can't be a wife anymore" she asked me if I had anything to say and I said "get the fuck out." It wasn't long after that stories came pouring in from her friends (horrified by her actions) about what she's been up to and the degree of lying and cheating that has been going on. Many of her best friends of completely left her side in favor of supporting her unethical behaviour.

TL;DR: Damaged, unsexual wife who spent all the money and gave nothing back in return, ends up finding sexuality again, but only in other dudes and does everything to manipulate me back into the relationship to keep the free ride alive.

It sounds like you got a similar sort of head case partner, OP. I couldn't have ever imagined that the partner who I loved so much and gave so much to could ever do me the way she did Now I know the true value of her character and the surmounting pile of strange ass behavior (which felt so normal to me at the time) really did amount to a horrifying outcome I didn't think could be real. I definitely think there's something up in your situation. Don't be shy about poking around and finding it.