Well, I am a bisexual and my wife knew. We had discussed many times about experimenting with others. She did find it exciting when horny, but would go back to it just being sex talk, otherwise.
Once, while we were about to move our house. I suggested to get a nude massage for both of us from a guy. (We had taken couple massages earlier by girls, and also given ’em a light show, thats a story for some other time).
Cominng back, she liked the idea, but was still hesitant, and was asking me to take one for myself with a happy ending. (As I said, I am bisexual, and she knows like guys stroking me or sucking my cock).
However, I wanted her to experience another guy touching her. So I agreed to her, about getting a male to male masage for myself. But asked her to watch, at least for sometime. And if she wants, just get her legs massaged. So she doesn’t have to loose clothes, but just a loose shorts will do. ( I discussed the same with masseur and explained to him about my wife’s reservations, and told him to make her comfortable)