They can feel emotionally distant
So, it turns out that men don’t always want to have sex. If they’re going through something difficult, they feel emotionally removed from their partners. When my partner is under a lot of stress, he doesn’t want to have sex because he feels weird/bad about being physically close to me when he knows he’s so mentally far away. He says it feels like a lie. That is actually rather considerate, when you think about it.