don't touch just watch

My boyfriend and I would love to spice up our sex life by having a "foursome". We actually are quite jealous and nervous, so that's why we first would agree on "just watching": What I mean by this is, that I fantasize having sex with another couple in the same room. With a couple that are our friends. What happens while we're having sex next to each other is, that I am beginning to kiss the other man slowely against our agreement. Secretely I always wanted to have sex with my friends boyfriend once.. And finally in the heat of the moment we can have sex with each other and maybe even telling each other that we are in love with each other without being illoyal to our patners in that moment...