BPD - In the Middle of a downward Spiral

I have been up all night and as i feel im losing my grip on everything, i need help. I have been seeking professional help and calling lifeline and such but i am still at a really low point and cant find a way to escape.

My recently ex-partner has been recently diagnosed with BPD. The break up and diagnosis came about because of an affair on their behalf. It had been ongoing for a few months, and while i found out very quickly, each time i tried to work through the issue and move forward with them, it kept happening. The affair started as a long distance thing, over phone, messages, pictures etc. but by the end had turned physical (i didnt know this part until after the relationship ended). I felt that while this was a betrayal of trust, it was something i wanted to work through as we had been together for over a decade and have children together.

I ended the relationship on the forth time i found out in the 2 months it had been going on. It had gotten to the point that i was starting to have panic attacks because my gut knew things were still happening and i didnt want to believe it. The lies and deceipt were so deep at this point that while they knew i was having panic attacks and was seeking medical advice, they kept up the lies and made me feel like it was my fault for not trusting them. I cant come to terms with how much my partner has changed.

They moved in with a trusted friend. The kids stayed with me. I wanted it to be this way to protect them from just how unstable my ex is right now. The kids and my ex both thankfully want me to be primary carer as i have always been the more stable, loving person of the 2. Looking back now i can see that this issue was present in our relationship probably the whole time we were together, just in different ways (money, food, power struggles to name a few).

Within a day of the breakup, my ex was coming over. They visited everyday, having dinner with the kids (and me) and putting them to bed. Most of the time that they were at my house, while suppose to be seeing the kids, they would follow me wherever i went and would leave the kids to do whatever. I called them out on this, let them know that they arent here for me and should focus on the kids. They cant. They were chasing some sense of normalcy and essentially wanted to keep the door open with me, "in case they get better". The fact that the relationship with me was more important than the kids really shocked me. All i can think about right now is making the kids lives as stable and safe as possible and the ex is chasing me instead.

I wasnt against the idea of getting back together sadly, which i have been told (by professionals i might add) makes me an idiot and a dupe for not protecting myself better. I didnt realy want to think like that until we sat down one night and talked about the fact that the affair is still ongoing, that it had been physical and that they were still meeting up with this person for hook ups. I asked them to stop, i said that they can have everything they say they need, like their own house, to be single, access to the kids, whatever, if they can just stop and focus on the themselves and the kids for a few weeks. If the new relationship continues after that so be it, at least we can take the time to get some help and catch our breath. They said that they would try and focus on the kids more. I pushed the point and asked if they cant stop themselves or if they wouldnt stop themselves.

The response still eats me. They said that they wouldn't stop, that they just want to be selfish and that they cant think of others first, even the kids.

My ex's relationship with they family has suffered hugely because of all of this. Several of their siblings have put distance between themselves and my ex. Im not sure how their parents feel exactly but it mostly seems to be shock and sadness and inability to figure out why.

The hardest part for me right now is that while i just feel sad for my ex and want to help them, especially since their family isnt in a good spot now, i also know of an upcoming meeting between my ex and the other person and it cuts at me. This is so fresh and raw and to know when things will be happening and to be powerless to stop them hurts so much. I cant get it out of my head and my thoughts keep trying to figure out how i can get them to stop running, to stop making bad choices and to think more clearly.

I know logically that i cant. I have read enough online to see that i have no power or control in this situation. This is does not help me accept it at all. I am so lost and confused and sad and angry and i dont know how to cope with this. Nothing here seems rational or logical.

I honestly hate using forums (not these ones specifically, just as a general rule) because it is so hard to get the detail and point across that im trying to make, too much room for misunderstanding but ill do anything at this point if it helps me cope and learn to understand what i can do for me, the kids and my ex.

Please dont hate me.