My boyfriend and I were at a party at the home of one of his coworkers. One person at the party started using offensive homophobic slurs, so I asked him not to use that kind of language. He persisted, and the conversation escalated into an argument. My boyfriend did not take a position, and he later said he “didn’t want to get involved” and that it had been “none of my business” to stick my neck out against the bigot. I believe that silence implies acceptance. Though there may not be a moral obligation to intervene, it still seems like the right thing to do. What is the moral principle behind this? Is it important enough to end a relationship over?