My wife's best friend and her husband want another child and want my sperm donation via sexual intercourse with her. The issue is whether or not to tell my wife?

I'd think you'd want your wife in on a decision like that. If it was me...and my husband did that sort of thing behind my back....he'd be divorced! It's best to be upfront about that sort if thing, at least if you discuss it she has the chance to say no!