Welcome pinkfreud,
you are looking for guidance. BPD is a perplexing condition and some of the guidance may be perplexing. It takes a while distance yourself from what has been said and done in the past moments and see the bigger picture.
(1) I am by nature a very tough and resilient person, but the pain is real. It tears at my heart to hear her say so (2) many awful things, destroy personal belongings, threaten suicide, etc., but yet it is also (3) painful to see the person I love suffer that pain as well. She will not get help. All counseling sessions have been, in her mind, (4) to get me to change. Fortunately, I have.
1) You seen yourself strong and your strive to be strong. This is good however it... .
2) ... .drives her to extreme strong measures as well. You are so strong that it takes suicide threats to shake you.
Note: This is a common dynamic, don't blame yourself. There are ways to break this arms race.3) You are sensitive and reactive to her pain. Which is good but at this time enables her to manipulate you.
4) Change is good. Not sure what changes happened though. Her guidance is dangerous here. You need to be at the helm.
You are a strong and sensitive guy. You can be a good partner for a pwBPD but only when your sensitivity is not used as a weapon against you and when your strength is not used to destroy the relationship. The key change needed at this point is for you to develop skills - see the LESSONS post and the related workshops. Skill learning requires exchange so also post on the board.
Breaking the I'm strong / my pain is infinite arms race: You can see her pain. You can't fix it. It is hers. Only she can tackle it. The only thing you can do is validation. Use your sensitivity to sense. Use your intelligence to express. Don't fix anything! Don't feel responsible. Expressing her pain helps you to expel some of it from your mind - where it would do damage laying around unprocessed. Her hearing that you heard helps her a little. More can't be done by you. You may find
this post useful as it also illustrates how pwBPD manipulate others to provide them unhealthy validation (pwBPD feels pain and forces partner to add to it while vocally playing victim).

,
a0