Good for you. It's a process, and a very tough one indeed.
I can relate. For the last few months, my husband stated that he was planning to stop paying for one of his BPD daughter's recurring expenses. Like you, he informed her of his plans, "After your next birthday, I'm not paying your recurring bill anymore. You're an adult, it's not appropriate that I continue to pay your expenses. I'm retired, I can't afford it."
Well, that was the plan, and she reacted in the expected way--with avoidance and cutting off contact with him. But what has since happened to the plan? Her birthday is coming up in a few weeks, and my husband has already walked away from his "boundary"! He didn't stop paying for one or two months, to gauge how she would react, to see if she would work out a solution herself. No, he has been walking back his boundary, early: "Well, I'll still pay for half." My guess is, he'll be right back to 100% by the time her birthday rolls around. Why? He can't stand the guilt, the begging (via her therapist), the ongoing estrangement. He had declared his plan and gave her a long runway for her to adjust, but when it came down to it, he couldn't hold his boundary--he just can't shut off the ATM. In her eyes, he's always there to rescue her, and in her opinion, he deserves to PAY retribution for her supposed terrible childhood! Meanwhile, she feels entitled to live beyond her means. And he's trying to buy her love back.
That's why, sometimes I think the best plan isn't to talk about plans at all, but just to shut off the ATM, or cut up the credit cards so to speak. If there's a frantic call about new tires for the car: "I'm not fixing it, it's not my car, and I can't afford to take care of someone else's car, you're going to have to figure it out."
Look JsMom, one of the biggest gifts you can give your child(ren) is not to make them to bail you out of financial trouble as a retiree because you didn't save enough for your own retirement.




?). She told her siblings she would be doing so, not me. She also asked her stepbrother if she can stay with him when she comes for graduation. I feel so hurt, I feel grief, loss, anger. I also feel some relief if that's the right word. Relief that the terrible thing she's been threatening since last summer has finally happened. Relief that I'm getting something of a break. All I can do is build skills for when she reaches back out, which I fully believe she will do. Nobody else is going to be the endless supply of support and reinforcement that I have been, nor is anyone else going to be the target for her extreme aggression and anger. I suspect the best course is not to engage further as it may only exacerbate things. The only way to let her know that I understand and she can take all the time she needs is by letter.