You have a friend who trusts you to be honest and open with him/her. You've had something on your mind for awhile that involves that friend. The friend isn't doing anything bad or that would negatively impact your friendship. You can't talk about this with anyone other than that friend as it's a very confidential matter. Keeping it to yourself is starting to stress you out a bit and the stress level will likely increase the longer you keep it bottled up, but keeping it to yourself does not do any harm to your friend. Telling the friend what's on your mind may ease your stress, but it may not be in the friend's best interest (or yours) for him/her to know what's on your mind. Telling him/her could possibly cause tension between you, or it may be just fine and you'll laugh it off.
Do you tell? Or do you keep quiet and hope things work themselves out?
I think I know the answer but it would be nice to hear other people's thoughts.