I was in an "open relationship" for a while. After putting up with that shit for a year, we stopped, and went monogamous. We eventually broke up. It doesn't work, kids, except for really, really ugly fat people. Every open couple I've ever seen has wound up broken up, usually over jealousy, or one or the other of them finding someone else more interesting.
You are jealous for a reason. Your psychological makeup is hardwired this way to ensure the evolution of the species - men and women are competitive for each other because that way, the most attractive and hardiest people wind up reproducing, and ugly, unhealthy fatties don't.