I had sex with my wife's best friend and with full knowledge of her husband to provide them with sperm for another baby. Should we tell my wife or keep it a secret?

It would have been proper to talk to your wife about this before you did it. You should tell her and explain yourself. If she finds out somewhere else about it, you're going to have a battle. Something like that should be discussed between all four of you before you do anything. I suggest you tell your wife as soon as you can. Keeping it secret will only cause a major problem.

If your friend wanted to use your sperm to become pregnant it should have been done through artificial insemination, not the way you did it. What were you all thinking? Yes you need to tell your wife asap and hope that she can forgive you and give you another chance, although I don't know if i would be capable of either. 

Good luck, you're going to need it.

You should have told her about it BEFORE hand. If I was your wife/  girlfriend I would be mad. You need to tell her, cause even if it was just to provide sperm, it's still considered cheating.

If this isn't a bunch of BS i have to say it's a little late to mention it now.  You really don't have a marriage and your wife really doesn't have friends.

Sure, "Lie, deceive and commit adultery by having sex with your wife's best friend AND conspire to father a child without your wife knowing .. What harm could THAT do?"  .. SAID NO ONE EVER!

On what planet would THAT be O.K.???  THAT affects your entire family .. and your wife deserves to know just how far you would push your limits to risk it all.