Who told you not to, the shitty manager man? I've been through layoffs and I think it's kind of traumatic to be let go and then not have any interaction with coworkers if you were on friendly terms beforehand.

Yeah, I would just recommend not beating yourself up too much about this since you didn't know -- and couldn't know -- what would happen. It's only through encountering and experiencing these very negative outcomes that we learn to act and behave differently.

If you're brave enough, you could reach out to your old boss to explain your error and to try to repair that relationship. That could be a very scary but healing experience.

This manager could have just been looking for an excuse to fire your boss so I'm not sure to what degree you should be blaming yourself for the whole ordeal.

There was no way for you to predict how this would be handled and the manager of your boss handled things terribly based on what you've shared here.

There are probably other factors and context related to this decision that you just won't be able to get much insight into. How come you've leapt so quickly to the idea that your boss's firing was 100% on you and not a combination of different factors including the higher level manager being some big jerk?