You say you want a triad. A triad is 3 people in an intimate relationship. That means 3 people being intimate any way they want. That means 2 of them could be having sex while the other is off grocery shopping or traveling on business.
In a true triad, it is impossible for 2 of the partners to have sex behind the back of the other partner, because the freedom to do what they want is there. The rule that says "we can only have sex when its all 3 of us" is based on fear. Fear is not freedom. It would help you to decide what you really want, and talk about your fears more, rather than making more rules to protect you from your fears. What you have here is a "yes, go ahead, but not really - ok, but only when I..." situation.