I'm not really a HanLuke shipper but I can imagine them hooking up early in their friendship & then Han later after various revelations having a personal crisis over whether or not it's weird to have sex with both halves of a set of twins
& like he can't ask anyone if it's weird without admitting that he's already done it. he could talk to Luke about it bcos obviously Luke already knows but he's kind of avoiding the subject with Luke in case drawing attention to the fact that he's dating Luke's sister prompts a shovel talk. he's pretty sure Luke can kill people with his brain now and he doesn't want to have that particular shovel talk if he an avoid it.
If Han came to me with this kind of question, I would be very supportive and make sure he didn't uncomfortable about having to ask the question because most of all this is about his feelings.
However, I would also desperately need to know if Luke used the force on that thang, and Han also knows I would ask, which is why he never brings these problems to me.