I am in a private group for non's who deal with BPD family ex's, or spouses.
I find this very common among many, when they feel guilty to say they are walking or you want out and they want nothing.
Maybe and hopefully not case here but usually due to cheating, moving on etc, if they sign right then no problem legally. But most come back and change their minds, and want all, most, half etc. They rage, cry, scream, change their mind constantly till this is all done. Usually high conflict which you will find here and reading up. The LC is due to quilt but changes when they project later, deregulate, or rage.
My stbxUBPD, was what I thought ill with disability. I always took care of everything, when got to point he was getting at least better, started asking for some help for me, to move etc, because I was ill ( from stress no doubt... .

). He deregulated, had a miraculous ( see eye roll here) recovery, went on to cheat, ignore kids, hurt them and myself and want a divorce on his 1000th new GF timeline.
His new girlfriend ( of many online before her) has many issues is harming her children( by making all about her), her husband ( seperated) has no idea, according to sources she has had problems for awhile, and many affairs as well. She thinks him doing his responsibilities is enmeshment... .I am astounded that there is no morals or integrity in many of these people. It is all about them I know she is NPD as well. "I want the fantasy, I want him, I want her, never about their kids, responsibility or morals".
I want divorce have no problem giving but wanted what was necessary to take care of children and myself and what I am due ( I paid for houses, most everything, got him out of debt). But wanted fair to him as well, he kept saying no take all, thinking he could go with GF. You are going to hate me. Then back to not doing what he agreed to, help finish anything, to wanting it all, to crazy proposals, to threats and scary threats.
I should note upon counsel ( legal and otherwise) I realized I have to stop caring and being so nice. What he is leaving me in is a mess, and what he thinks he is giving is what the law probably would give due to all I have done, paid for, needs done, how I have furthered his career and left him in good standing credit wise, paid off all his debts etc.
He in fact should be doing more but will see probably won't have any idea I am really entitled to it and the mess he is leaving me in. Never would have bought the other home near his work, thought I had to care- take etc. What a mess. But all is good, I will be fine, and God will bless me through this as he will you. I will just have to have the faith and keep going for my kids and myself, be free of the situation and go forward.
Now after ranting, raging, hurtful things, threats, no help or cooperation, to me finding spying, he and his GF are so irresponsible in their fantasies should not have either of their kids, and more weekly raging... .
Now he called me other day, being kind, romantic and talking intimate things which just are strange. I had to just get off phone. He then called in front of people in a public setting talking to me about his personal body parts, then giggling and trying to make small talk. Again... .had to get off phone. Have no problem being kind, compassionate, being friends but have to remind myself that is probably not case and will be raging within days.
I have to remind myself I didn't cause this, have done right by him, taking my responsibility seriously and won't let him or her off hook. Maybe they found out I am going to hold responsible, and know about spying etc.
Now I am trying to deal with legal things, find out how he is spying and could put him in jail with possible felony and he is being sweet. I am sure will be raging again in next few days with threats.
I guess what I am saying is be prepared, you have children that more then likely you will have to be the stable, responsible one for. Make sure you have a back up plan in place for their care while you are at work, in case she runs off to fantasy land. More then likely that crashes and burns with 4 months to 2 years, then they want back etc.
Get legal in order what you need, want, and what she wants and have her sign or she more then likely once quilt passes or her new crashes will want more then you will be able to give.
Good luck. Sorry for what you are going through. There are so many books recommendations, tools, articles as well as posts that might help you.
Keep posting, many here can help you get through the tough times.