Hello amarie: I don't know as I have any particular suggestions with regard to how to talk with your therapist about the possibility of your having BPD. However I see this is your first post here on PC. So... welcome to PsychCentral!

I hope you find the time you spend here to be of benefit.
I've never been diagnosed as having BPD myself. However I once read the book:
Lost in the Mirror by Richard Maskovitz. And based on what I read there, I thought it was possible I might have been diagnosed as having had it when I was young. (I'm an older person now. And I've been told BPD tends to "burn itself out" as one ages.) Anyway... what I did was to take the book in to my appointment with the therapist I was seeing at the time so I could use it as a starting point for discussion. Perhaps you could do something similar? You might also make a list of the ways in which you feel you "fit" the criteria for BPD.
Another idea, if broaching this subject just feels too difficult for you, would be to write a letter. Then, perhaps drop the letter off prior to your next appointment so that your T has an opportunity to read it ahead of time. Yet a third possibility might be for the two of you to watch a video on BPD together. Two options for this might include family therapist Kati Morton's videos on BPD & quiet BPD. Here are links to these 2 videos:
Anyway... these are the types of things that occur to me. Perhaps other members will have other suggestions. My best wishes to you...