My husbands farts smell different. Is he cheating on me?

My husband is spending a lot more late nights at work. As a result, he isn't eating well or exercising. He mentioned his assistant, Andrew, is openly gay and kind of into him. His farts smell different. Does this mean they are having gay anal sex?
He also has mentioned pain in his rectum but always excused the pain as a result of his poor eating habits because if working late.

How can I ask him? Is this too touchy of a subject for most men to talk about with their wives?
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Please? I need advice.
My husbands farts smell different. Is he cheating on me?
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