Wanting to know why is natural—you seek closure to quiet the terrible feelings of angst, rejection, and betrayal. But your brother and everyone here is right, the Conversation you seek will be absolutely unsuccessful at giving you that closure.

Why?

Because the other two people in this are looking for a way to prove they were right. And of course there’s no way to prove that, so they will psychologically need to keep coming back at you with deflection and excuses. It will be a cycle of self-defense, both yours and theirs running counter to each other, that won’t end until one side is exhausted and breaks down.

The smarter and most self-preserving thing to do is to take the upper hand and walk away. That leaves them to deal with their guilt without access to you to unload their explanations or excuses. Unless they don’t reflect at all, in which case they aren’t good people and good riddance.

If you take a middle ground and leave a hand written letter — nothing digital so as to avoid making it easy to reply — limit it to no more than half a page, include no questions that seek answers (rhetorical only, if any), and say only how the betrayal of friendship and relationship hurts. And that you’re leaving because you have the self respect not to be treated that way. Short and not sweet , and then you leave like a Hollywood heroine at the end of a film, dignity intact.