Bijan doesnt get along with his best friend Mikes girlfriend, Yasmin. When she and Mike began dating, Bijan had a bad feeling about her almost immediately, but tried hard to give her the benefit of the doubt. However, as months went by and they all spent more time together, Bijan started to catch Yasmin in small lies that she wouldnt admit to, noticed that shed sometimes make petty and meanspirited remarks about mutual acquaintances, and felt uncomfortable with what he perceived as her subtle contempt for those less privileged than her. It also seemed to Bijan that Yasmin was slowly attempting to separate Mike from some of his friends and even family members, each of whom she seemed to have some small problem with. In his most cynical moments, Bijan speculated that Mike was only interested in Yasmin for her good looks and hoped they would break up. At other times, though, Bijan told himself to have more faith in his friends judgment. They seem happy, after all, he thought. Maybe I should just let this go.
Now, Mike and Yasmin have just gotten engaged, and Mike has asked Bijan to be his best man. Bijan feels torn about what to do. He is not sure whether he should be fully honest with Mike and reveal his feelings about Yasmin. On the one hand, Bijan is almost sure that Mike will be devastated if he shares his misgivings, and he highly doubts that his remarks will change Mikes mind about her or the engagement. Mike is so head-over-heels for Yasmin, in fact, that Bijan suspects that saying something would be far likelier to lead Mike to cut off contact with him than with Yasmin. On the other hand, Bijan feels that it might be his duty to speak up. If I dont do this, no one will, he thinks. Im Mikes best friend. How could I live with myself if I say nothing and he ends up in a miserable marriage to a bad person? He also wonders whether if he doesnt speak up, he should agree to be Mikes best man. On one hand, it would seem dishonest to agree given his feelings about Yasmin; on the other hand, it would be difficult to turn Mike down without being able to give his true reasons for doing so.
You havent learned ethical theories yet, but you are good at ethical reasoning. 

What should the people in this case study do? 
Justify your answer by sharing your reasoning why you think people should behave in certain ways.