Akizuki-ke no Jusei Irai -Ninshin Suru made Kurikaesareru, Tsuma to Ani to no Sex-

"He was only supposed to be a surrogate." The tests proved it: a would-be father couldn't bear children. It was a bitter realization, but that was nothing compared to watching his beloved wife f*ck his brother every day and fall in love. "You don't both have to orgasm...... why do you keep going....... why would you do this to me......"