What are your thoughts?

Assume u know both parties (a couple).. both are ur friends, A and B.
And u saw B with someone else with intimate behavior.
Will you : Tell A what u saw? Pretend nothing has happened? Tell someone else?

Assume u have told someone else and he/she in turn told A about it.
A confronts you.
Will you: Tell A what u saw? Avoid A in every possible way?

Now.. think the other way round.

Assume you are A.

Assume your friend told u C saw your bf/gf with someone else.
Will you want C to tell u the truth?
Or will you choose to ignore it?
Or will u confront your gf/bf saying that C saw him/her with someone else?
Or will u prefer you had not been told anything and continues your life being in the dark?