I am so sorry for your children and you.
You say you didn't see this coming. I was complaining in therapy one day about AH and his mother and how they wouldn't respect my schedules and timelines for visitation...
and therapist said this: What do you know about XH and his mom?
me: they are erratic.
T: that's right. erratic and unreliable. Now you know. Expect that.
When my son had the surgery we talked about and he woke up asking for his dad, I said to myself (seething, btw), this is THE LAST time I will be sitting around wondering where he is and when he is going to show up.
I was NOT going to have my children jerked around like that anymore. It was awful to see them at the mercy of the stormy, unreliable being that was my AXH.