Havin been in a long term vanilla relationship, I know that it is hard to know if you can trust your partner. No matter how long you have been together, there are little things that bring up mistrust and negetivity between each other. In my long term m/s relationship, I put ALL of my trust in my Master. I do it every time he wraps his hands around my throat, every time he tells me to cum for him. That level of trust is something that, while some people may be able to find it (and congrats if you have), I have never seen it in a vanilla relationship.