How to Do It It’s never been the same. Photo illustration by Slate. Photo by Gratsias Adhi Hermawan/Getty Images Plus.  How to Do It is Slate’s sex advice column.  Have a question?  Send it to Stoya and Rich here.  It’s anonymous! Dear How to Do It,  My husband had an affair many years ago. We have been married for 25 years, and his affair lasted at least four years. I smelled that they had engaged in oral sex years ago, and I cannot have oral sex with him again. I think about him doing it with her, and I am turned off. Am I wrong? Sex is good otherwise, just no oral. —No 69 Dear No 69, Is your husband telling you that you’re wrong for having this boundary? I’m not sure where else the question of whether you’re wrong would be coming from, so I’m assuming he may have mentioned it. He had an affair, which is a deep betrayal, and that left you with negative associations with the act of oral sex.…