someone may know about something you have done that you don't want found out.

The worry about whether someone will find out something that you believe will discredit you in some way is very damaging to you. It is much less damaging if you know that your secret is known, or know that it isn't known.

It is important that this worrying doubt be resolved in some way, in any way, as keeping it with you causes you to subtly destroy all your relationships. It will cause you to be critical of others, and to create distance between yourself and others in an irrational, automatic attempt to hide whatever it is that you feel cannot be revealed.

The simplest way, (but perhaps not the easiest to find the courage for), is to be honest and apologize sincerely if it is something you are sorry for. Whatever unpleasantness that might arise from this revelation is now outside you, and can almost certainly be resolved relatively easily and objectively.

Failing this direct approach, you could find out for sure whether they know or not. It is the uncertainty that is most damaging, so removing that is a valuable "first aid".

Even if you are worried that should someone find out about you it would hurt the other, your concern may still be a worry about your being discredited. You are worried lest they know it was you who "did it" and caused the hurt. Handle this as above. You will need to find a little courage!

If it is not possible to do the above find someone whom you trust and tell them EVERYTHING.

It will help to use the "Critical" handling steps.