sheepdog, you have a lot of your own feelings to deal with around this guy, what he did to you, and what you did with him. Plus a bunch of doubts about what sort of person he really is, given his public facade about his new relationship, and some fears about what he could disclose about you. there is still a lot to unwrap in there.
Here's the some other stuff you mention:
The BPD I had in my life and I have not spoken for over two years. I have zero desire to ever speak to him again.
I have been waiting for the friend who was in our triangle to get another job so I can delete her on FB but now he is friends with so many of my friends.
Now that he is friending (or they are friending him - not sure) many of my friends, I have to see him or posts friends like with him much more.
It makes me feel unsafe again.
There are some practical/technical solutions in this area. Here goes:
You know that it isn't healthy for you to ever speak with him again.

I think that seeing what he is up to on Facebook isn't healthy for you either.
You can block his profile on Facebook. Almost all of what you see from or about him will vanish. He won't be able to message you or send you a friend request, or see anything about you either. If a mutual friend says something about him, you will still see that, but 90% of it will go away. (I know--I've blocked one toxic person on FB, and it helped me a lot.)
Blocking somebody or just De-friending them is visible, even if not shown to them immediately and somewhat provocative. It probably isn't a good idea to do this with your friend/coworker, at least until she gets another job.
You can also unfollow someone on Facebook. They aren't hidden from you, you aren't hidden from them. Her posts just won't show up in your feed. If you are curious, you can still look at her wall. Doing this with her sounds like a good way to make yourself feel safer.