Keeping secrets is OK when:
- The secret will not damage the relationship
- The secret is known to you and you alone
- The secret will not damage your partner
- The secret does not violate the trust of your partner
- Keeping the secret will not eat away at you.
You can not keep secrets that others share. Others are not under your control.
If the secret has the power to destroy the relationship then you should consider which is more important. Some relationships are just not to be.
I believe that the most important aspect of a relationship - lover or friend - is trust. So, ask yourself, "Will keeping this secret strengthen the bond of trust or will sharing this secret strengthen the bond of trust?" Choose that which strengthens trust.
A secret which is very dangerous to you, them, or the relationship may be impossible to either keep or share with out loss. Losing a relationship through honesty is better than maintaining one through deception.
Always consider what is best for the other person. Place their needs, safety, feelings before your own
Such decisions are not to be taken lightly. Some, few, situations just do not have a win-win solution.