Is someone else’s behavior ever a circumstance?

In an earlier answer about a situation, I was told to put the C as “I live with this person.” I think I was mixing thoughts and behaviors. I made not talking to me mean, not liking me.

Maybe my situation is about creating a boundary. Is there a resource available that guides me through setting a boundary? I have two situations for this:
1. Flatmate not speaking to me.
2. Friend’s boyfriend always telling me about terrible things in his life and how wronged he is. If I don’t agree with him he reacts (email rants, uninviting me to show my art to a large exhibition, etc).

I have somewhat regular interactions with these people and don’t know how to interact? Maybe I am wanting a good outcome and I have to stand in my truth and let the outcome be what it is?