You can answer it quantitatively. Look up on Google Scholar how much stress contributes to the illness he has. That's your upper bound. Then reflect on how muc

You can answer it quantitatively. Look up on Google Scholar how much stress contributes to the illness he has. That's your upper bound. Then reflect on how much stress you have caused him. Multiply and there's your answer. You can then split your contribution into the necessary (stemming from his inability to handle disagreements) and unnecessary parts (stemming from you being a prick or a bad communicator) to determine how guilty to feel.