Hey Cassia! Welcome

Being involved with a BPD person myself, I can totally understand the toll it takes, it's certainly not easy.
Blocking him is not necessary, I think. If he engages in "vitriol" simply don't engage at all! It's very important not to make matters worse.
If he texts you something offensive, you can respond by saying:
"I can see that you are upset/angry/whatever. I don't want to continue this conversation at the moment" OR "I'm going to check up on you later" (depending on what you want to do) and ingore him for the rest of the day, for instance.
(there's probably a better way to do this, as older members will tell you, but it's important not to engage back!)