6 years destroyed

She has quiet bpd. It was a rollercoaster but she had gotten so much better the last 2-3 years. The splits stopped turning into blackout drinking and screaming matches. She didn’t leave nearly as often. She could rationalize when her feelings weren’t real and would take space.
Then something happened; I’m not sure what besides the anniversary date of a traumatic event. Over a couple weeks she started declining so badly that the worst split I’ve ever witnessed started. She said she didn’t have it in her to fight it anymore, and she was going to let the “darkness” and intrusive thoughts win. She told me if I knew her thoughts I’d hate her and would want to never be near her again. She went to stay with her mom so she didn’t hurt me or the kids and to try and sort through her feelings; but instead, she started sleeping with her coworker 4 days later.

This is far beyond her character or values. It’s a complete 180 of anything I’ve ever know in our 6 years, even during the other splits. She says she feels nothing at all and that she can’t fight for us because she can’t even fight for herself. She adamantly denies the sexual relationship despite me throwing literal proof at her. She ranges from stone cold and mean, saying we don’t get along and she wasn’t happy with me; to saying she knows she lost me and ruined us because she couldn’t get herself together and it’s her fault.

It’s been almost a month now. Shes still sleeping with the coworker, who is younger and also has bpd and is going through a split up. We don’t speak and I’m trying to mend my heart and my kids hearts. She cried when telling them she wasn’t coming back the other day (which was a conversation done out of anger when I put up a boundary that until she’s more stable I was restricting access to the kids. They’re my kids she’s helped me raise for 6 years).

Apparently the relapse is 10 times worse she says. I read so many BPD stories, and she doesn’t follow a lot of the patterns. She was doing so good. We were talking about a third child together and our wedding. We had just came back from a family vacation. Our sex life was improving after a really tough period.

Now she left and feels like a ghost hovering above her body watching herself drown she says. She’s able to sleep with someone else and put time into that. Actively lie to me, and destroy 6 years and our family.

I’m not sure what I’m looking for here, besides maybe just venting. She’s not a shitty person, but she’s doing really shitty things and I hate this disease so much because I know full heartedly that in her right mind, she would never allow herself to be who she is right now.