I still work with her in a small organization, which at times, especially in the first 3 or 4 months made recovery difficult.
Well done on your recovery so far. It's not easy to do the acceptance or letting go when you see this person frequently during the week.
If I ever think about our relationship, it's typically about all of the red flags I refused to see, and I thank my lucky stars that I broke free of that toxic relationship, because it was killing me.
I do think signals that something else is there that isn't what we may want in a relationship are important. Well done on seeing those, and recognising the negative effect it had on you.
Many relationships with pwBPDs can cause undesirable physical effects in the non's body. I do think when one consciously releases oneself from such a relationship, it has a liberating quality. There was a spouse of a member here (not the pwBPD) that mentioned the non she was dating (the partner of the pwBPD) got a dx for a critical illness below 40(?) and passed away. A lot of us don't experience the tremendous healing from such a horrific state of body, but what we do have is a position where we are at relatively lower risk of disease. That is, the links to the causes are reduced, so there's blessing there. We don't often see that. That helps me see that "stars" that helped burn much brighter than we may first perceive.

I think it's recognising what you call a refusal of seeing that's also important. Did you figure out why you had a tolerance for those things or a want of denying the things which you now call red flags?
It was like we were all auditioning for the next tragic victim/coping mechanism in her life. I am so glad I did not get the part!
I do think that's a relief for many people here. When we have the hindsight and being outside of the triggering by the issues--we then may realise that we're in some way very blessed that we didn't stay for a long time in that relationship.
I hope you're enjoying your peace.
