While we were together I tried to use every technique I could, but she could see through them.
a lot of us run into this problem. why? well, its awkward learning new ways of communicating, kind of like when you learn a new essay format, it feels very forced. and it does to the audience too. or often times we use them in a way to sort of "make the trouble go away". the key to the tools and the communication techniques is both sincerity and authenticity; using them in a natural way, that sounds like us.
i dont say that to monday morning quarterback. i say it because the tools will take you far, if not with her, with other relationships (of all kinds) in your future.
it reminded me why I should not be sad she is gone.
in my experience there is little point in fighting the sadness, or any of your feelings. i went through a spell where i believed something was wrong with me for missing my ex, for still loving her. but thats the way that grief works. i learned that if i could accept my feelings, i could work with them, process them. if you can do this, it will help keep you grounded.
the fact is that youre both sad the other is gone, even if you believe its for the best. youre both grieving. and it shows in the ways youre both venting the hurt.
so what happened here? it sounds like she took you changing your relationship status very personally - it was a trigger. the same thing happened to me actually, even though my ex broke up with me. it might seem silly to you and me, but its a big showy deal for some people, and people with bpd traits very much live in the moment, and overreact. and it sounds like it jerked your chain a bit.
not engaging was one option. she lashed out out of hurt, probably eventually would have calmed down, and felt silly or embarrassed.
She chooses times when I have no mental capacity to be mindful.
you do, though, with practice. you only need to be as mindful as "i should sit on this, and think about what, if anything, i will do at a later point". and maybe that later point comes, and maybe it doesnt.
the bottom line i think, is that you share children and are going to be in each others lives to some extent for some time. ideally, and if possible, you will want to be able to work as a team, who gets along, to whatever extent you can. so long as youre both rehashing the old relationship fights, you cant; and it doesnt help either of you in terms of resolution, closure, or grief.