I'm so sorry he's with a new woman and texted you That's a horrible thing to have done to you.
Then a string of really abusive and threatening texts saying I'd abused him as a vulnerable adult by having a relationship with him - I feel really scared of what he might do next.
His fear of abandonment is triggered. He is projecting because he felt a perceived or real threat of being abandoned.
What scares you exactly? You know him best.