No is not gruesome, and I tell you why not. Have you ever heard people writing something bad about a person who died? You remember the good right? somehow all the bad memories vanish. In business they say to start with the end result and work from there to achieve what you want. If you want to stay together in this trying times than remember everything that is good and important in your relationship and than think how it would be if you would loose that person, just do the exercise, but make sure that you don't start this exercise after you had a fight or argument..