He lives on his own, while I support him financially
That is fortunate you can do that -- it's a serious disability and he may not be able to function in a meaningful way just yet. In a NEA-BPD Family Connections class, I remember they referred to BPD as a potentially fatal disease and encouraged us to not use the word "enable" because for many parents there, "enabling" was the difference between their child being alive.
Altho I think the word coaching is what we're going for

he suffers from mood swings, wild rages and sometimes paranoid fears. He keeps blaming us - his parents - for every misfortune, while demonstrating black and white thinking - I am being alternately idolized and condemnded as the worst person on earth.
It is really about him and his mood states -- they feel real and it can be hard to sort out what is real, what isn't.
How do you respond when he blames you for his misfortunes? There are some helpful communication skills that might be effective. I have found it takes some trial and error to figure out which ones work.
And what Huat says about taking care of yourself is so true! With a BPD loved one, taking care of yourself takes on a whole new meaning. In order to be an emotional leader, you have to have a full cup. When my SD20 lives with us, I guard my well-being carefully so that I can engage with her in a meaningful way. If it feels like she is being passive-aggressive (her style), I take that as a cue she needs to ride the roller coaster, and we can pick up when things are a bit more grounded. I don't try to debate anything with her because it's futile and likely to change. Instead I try to find something about her feelings I can validate and then focus on taking care of myself while letting her know I will be there at some other time, to avoid triggering too much of her abandonment fears.
It's a balancing act that does get a bit easier with practice.
Hugs to you, Kika.
You are not alone.
LnL