Tetra is what men hope their wives would be when it comes to taking on another spouse. Them being okay with you having your cake and eat it too.
Would any guy be okay with the person you're in love with to also be in love with someone else, even if that person is your best friend? I'd think you'd rather than just let your best friend be together with her and they be faithful to each other and you find someone else, or your best friend offers the same.