My husband has a tendency of winking at a friend of mine and calls her sweetheart. I am present when this happens and he is good friends with her boyfriend.

Is it a sign of interest or flirting?

He doesn't call me sweetheart or wink at me ��

If he is not mad, upset, or jealous, why are you?

If your husband and this woman were in the workplace, and he was winking at her, and calling her sweetheart, it would be considered inappropriate. If it bothered her, she could report it, and he'd be talked to. Whether it means anything, or is completely harmless.

So why is it okay for your husband to wink at, and call another woman sweetheart, in a social setting? Or any other setting- would he do that to the bank manager or his boss (if she were female), or his daughter's 10 year old friend for example?

If this woman's husband is aware of the wink/sweetheart comment, and he isn't bothered by it, and has actually seen your husband doing this, then for now, I wouldn't bother about it. IF he is winking and calling another man's wife sweetheart when her husband is not looking, then I'd have a talk to your husband and tell him to cut it out.