Well my friend. It sounds like you have come to the right place
Your story is not unlike others here who are on a similar journey. Yet there is a big difference, it sounds like you would make a great triad if everyone gave up the lying, deceit and needless assumptions and ownership crap. Ususally when people cheat there is no hope for a successful triad, with you three there is a big difference, because the cheating that is going on is between you all. Only because no one wants to fess up...
This could all be so possible if everyone started being honest. Why is that so hard for them and you? I don't get it. What is the purpose in hiding everything? It seems rather ridiculous that you are all going behind each others back to love each other when you all love each other. Its love! Love is good! Why taint it with cheating? Especially when it isn't a matter of one person is left out of the loop! You all love each other, usually people come on here cheating because one person IS left out of love. You don't have this situation, so give it up and start making plans to all be together.
I don't see why anything has to change here other than everything go from being underground to above ground. You can have your night/day with each of them and the only difference be that they know about it. If there are other boundaries that need to be discussed, discuss them. Take the bull by the horns and get talking.
I can't stress enough how this could be so wonderful just by being honest and open. I have never seen a situation that could be so right where cheating is concerned. Its actually making me have goose bumps to know that you could all have something so special if only you would all get over whatever this hang up is that you have....
Do some reading here and see what other triads go through.. start with a tag search for "triad" and maybe "cheating".. then I would suggest reading about how to create a healthy foundation for a relationship by doing a tag search for "foundations" and "lessons" you will find many ideas and can take or leave what you like... add to the list if you think of something else too please, as sharing what works is so helpful to others.