I try to validate his feelings... . and at the same time stand my ground and let him know that my past is my past and that I can't change it.
Hi MSE1081,

From what you said, I think you handled it well. You're absolutely right that there is nothing you can do to change the past. If it's an issue you have addressed before, you can tell him that you have already addressed it, you wish it weren't the case as well, but you will not address it again. This could be your boundary.
Unfortunately, when you are with a pwBPD, you will never