You need more help than we can give you. If your wife has serious psychological issues about sex, and your sex life is nil, than you are a long, long, long, long... long way from being able to include someone else. In all honestly, my suggestion would be to set aside the idea of watching your wife with another man and focus on your own relationship and sex life. I would strongly suggest marriage counseling and therapy to get to the root of your wife's issues and find solutions.
It's been said before and bears repeating often: swinging is not a cure for problems in a marriage or a sex life.