Here's all the truth you need:
Your WBF cheated and called it revenge even with the only evidence being your word against someone else's.
He has a drinking problem you're not sure he'll even address.
He went to some woman's house, practically a stranger, to "get dirt" on you, the woman he was trying to start a family with. He went to HER instead of communicating with you.
He intended to have sex with her and at the least very nearly did. You posted that he can't perform when drunk...apparently he was capable of an erection and the (allegedly) clear thought that he couldn't betray you again.
He is now expecting you to believe what he says over what she said. The exact thing he has refused to do for you.
To recap: he cheats, blames stories he heard about you for his actions. He makes choices to be on the path to again hear more dirt about you so he can again betray you but now expects you to give him the benefit of the doubt.
Do you love him or the idea of him? Because, to me, this is a man looking for a reason to cheat. Looking for reasons to knock you off of whatever pedestal he puts you on so he can justify being an asshat. His attitude and actions are unhealthy and bring big enough issues that even if the rest of your relationship is perfect, the drinking, lies, undermining you, cheating, lack of trust and communication issues are enough to kill whatever relationship you try to build.