Paul G,
Thank you for coming to BPD Family, we are here to listen to you and support you.
Having your affair partner with BPD commit suicide, and then having your wife find out about it can be exceptionally devastating.
Probably the best thing you can do right now for yourself is to find a licensed therapist and work with them on both the grief (loss of affair partner, and perhaps the potential loss of the relationship with your wife too) and understanding what it is like to be in a relationship with a borderline.
While you will have to answer for your indiscretions to your wife which will make your recovery much more difficult. Please know, that while you might have been the trigger for the suicide, you did not cause it, you could not control it, nor could cure it, and you have found out the hard way it is one of the more deadly mental health illnesses out there - I am sorry for your loss. Her taking her own life, was her decision, not yours, even though I am fairly certain you might think otherwise - and a licensed therapist is the best way to go on this. If you find yourself thinking of suicide for yourself, especially late at night, reach out to 988 (voice & text) or 741741 (text only).
https://margalistherapy.com/articles/borderline-and-narcissism-issues/handbook-for-dealing-with-a-bp-np/ summarizes on how to deal with a pwBPD, and there is a book that can give you a lot of insight into your own contributions to this dynamic.
The love you describe is more intense than a normal relationship from a phenomena known as 'love bombing' where she mirrors to you the ideal person that what you want, it is incredibly intense and forms a 'trauma bond' - both are topics best dealt with a licensed therapist as these are incredibly difficult to recover from.
My heart goes out to you, as you likely thought you were helping out someone in need and 'unintentionally fell in love' with them. Let me know if you are willing to explore this aspect more.
In the meantime while you are sourcing out a licensed therapist for yourself, to process your grief, trauma bond, and potentially other issues too, be sure to do self-care whatever that may look like for you.
Take care.
SD