My wife is similar to yours in the way of being shy and worrying about my feelings when we first talked about her fucking someone else. I won't bore you with a lot of background, but I finally got my wife to jump into bed with another guy, but the key is not to rush her into it. Talk, suggest, and with my wife, she finally said "if it happens, it happens, but it will not happen."
Well, we were out one night and she was in a 'good' mood after some drinks and, after urging her to talk to one of the guys sitting next to her in a Bar, I went to the restroom and took my time getting back. When I came back, she asked me if I would be all right if she did 'something' with that guy. So instead of "it will not happen" to "is it OK with me" ..... it happened that night.
