It sounds to me like he genuinely doesn’t care about your marriage and just sort of married you to go along with whatever you wanted. Now you want something different, and he’s just going along with that too. He genuinely does not seem in love with you. The fact that he really thinks you had sex with somebody else on your wedding day, and never confronted you before this, goes to show how little of a shit he gives. Same for the coworkers, friends, and brother. If he actually loved you, he would’ve said something before you brought it up. Obviously, this has pushed you to the point where you’re checking out too and feeling attracted to this “better” version of him. Honestly, you could go both ways with the brother. I feel like if you have sex with him, you could either 1. End up developing a relationship with him 2. Realize that it was just a stupid crush and move past it. Both of which each have their own set of consequences and repercussions. Or you could just not pursue it. Regardless though, this marriage is so over, and you should divorced your husband immediately.