Hi Sidney09 and welcome.
I join Panda39 in welcoming you here.
And I'm glad you've found this board. It certainly felt like a big relief in terms of self-awareness of my sanity when I learned of this site and its content.
Mixed feelings of relief and fear may come when the partner is diagnosed. There's a point of reference and indications of direction--that's relief. The difficulties along the way--there's fear there. You aren't alone in this.
Yes, exhaustion--especially that of physical and emotional exhaustion--is often a result of being in a relationship with a pwBPD. The heightened requirements of living with such a person can cause us to feel drained.
Panda39's right, you can understand BPD here. Apart from understanding BPD and your partner, you may also look at your own health and personal safety. So you may consider this alongside your reading:
https://bpdfamily.com/content/triggering-and-mindfulness-and-wise-mindA short video on what mindfulness looks like for yourself is here:
https://bpdfamily.com/message_board/index.php?topic=89910.msg604907#msg604907I hope you find peace and hope to hear how your progress unfolds.