I'm sorta new, so I'm wondering (guessing) you are the custodial?
My Dh's ex willingly gave up custody of her 4 girls (she actually demanded DH take them or she'd put them in foster homes) and for the first year, I beat my head against a wall trying to get her to be a better parent. She only took the girls when it was convenient for HER - never me; even when I was in labor with my BS, she wouldn't pick her kids up from school & take them to Dh's parents house while I gave birth - a neighbor of mine had to do it....
#1 You won't ever change HER. Give it up now and save yourself the Tylenol and therapy.
You absolutely CANNOT control WHAT that woman does or says. You can only change the way YOU react to it.
#2 Re-negotiate your "deal" with Dh regarding his child. If you feel there may be times when it won't be in your ss's best interest, or yours, for him to be in your care - Dh needs to step up to the plate and make arrangements.
I dont know enough about your situation/arrangement - but you sound VERY frustrated... And I can 100% relate - as I have BTDT, for many-many years.
At first, I took on the 4 kids willingly...but then, it became over-whelming for me and with no "help" from their BM, well, I then had to go to Dh and make it HIS responsibility. After all, they ARE his kids, not mine. I have 5 of my own. It doesn't have to be done in a mean or nasty way - but your Dh MUST realize that if the bio-mom won't do "her part" then he must pick up the slack and/or find some alternatives so you are not going
PM me if you ever need to talk more... I'm thinking of you....