Question

If you have these two good friends A and B. A and B are couples. A is seeing someone else while being with B, and you know everything. You are the good friends of both of them. You are faced with a decision that you must make, which could prove potentially tragic/fatal in the future. Would you...

(1)...be a by stander and act nothing has happen
(2)...tell B, because B is the innocent party
(3)...talk to A, to wake the idea up
(4)...do not do anything at all