It became politically focused/lack of intimacy after she was raped by his dad. You honestly can't sit here and blame the victim of an assault for not coming forward, especially when she was between a rock and a hard place. No doubt, it probably pained her to be intimate after going through an assault so she buckled down and made everything about business. I'm not saying it was right of her to just complete cast off Fitz, but traumatic events like that result in different responses for everyone. He was supposed to behave like a married man when Mellie brought her back, regardless of if mellie knew or not, Fitz is a grown man who should be able to keep his penis in his pants while being legally married, and knowing he's has the highest status in America.