Here we see Radahn reacting like a rational person when asked to become the consort of his younger brother who looks like a little girl.
In fairness, we don’t really see much of any indication that their relationship as consort and deity would be anything romantic. Or if Miquella just wanted to recruit who he felt was the most suitable lord as his representative. Less a spouse and more a champion. It felt the same way with Godfrey and Marika. Like he was simply her greatest warrior.