Ahhh Jac, I shouldn't be in these threads. I believe in inclusiveness rather than exclusivity. And I don't subscribe to the cult of sacrifice; instead I am for freedom.
A lapse of judgement or a screwup doesn't help the relationship, no matter if it's confessed or not. Once done, one may be able to fix things up by fessing up, or it may make no difference, depending on the circumstances.
RE: Does your partner need to know ALL of your friends?
Tell your future husband I'm your friend!