I think he finds comfort in sex. I read somewhere that he seeks sex when he is feeling down. He immediately sought solace from Charlotte when Guts left the Hawks. He immediately wanted to rape Casca when they rescued him from the dungeon when she was dressing his wounds. He wanted to rape Casca before the Eclipse. The sex with Genon is just for monetary purposes. That one he did not enjoy, but actually felt discuss. But then you see him scratch himself in the same manner after he had sex with Charlotte, which is confusing since he was basically preying on her and how he artfully made love to her body. But I believe that is from his own disappointment in not being able to get what he wanted from Guts rather than being disgusted by the act himself, because we know Griffith is depraved enough to take advantage of women and enjoy it.