do you/would you tell your partner about another friend's secret?  

No, I never betray a confidence so there are things that my husband still doesn't know about. My word is very important to me and, if I promise something, I will do it...keeping a secret from everyone included. Just because you're married or in a relationship with someone does not mean that you have to tell them everything that you know. If you don't feel that you can keep a friend's secret from your partner than at least tell your friend that before she confides in you.

I never did so .
Though we are unite in everything we have ,but this can't be in that extension,we have our own friends ,and also we should not betray every friend we owned.

I won't tell all the secrets of my friends to my husband. I might tell some of them. I don't think it is a big issue because I know that my husband is not going to tell that to anyone. I won't tell any other person my friend's secret.