My best friend (of nearly 30 years. I met him when we were very young) was also a piece of shit.
He was going through a really bad patch in life. He had been kicked out of his house and being divorced when he was caught cheating. He could only see his kids at the weekend but they didn't really want to see him etc etc.
Long story short: we helped in any and every way. We spent cash on distracting him and feeding him. Paid for a holiday for him. And he then back stabbed us on Facebook.
Now I don't have Facebook, and the wife hardly uses it, so we weren't supposed to see the shit he was trying to pull. And when I pulled him up on it we got the "it's your fault for seeing it" and "I knew you would be upset which is why I didn't tell you" type bullshit.
I wished him well going forward in life and then we blocked him on everything we could. And, my god, was it a relief.