But Ei has his reasons for pushing Gin away. He already made it clear to Gin that they will be nothing but sex friends so it's not just Ei's fault. It's not really his fault. Gin also has a choice to leave Ei since fourteen years is just so long. However, he chose to stay. He chose to be patient even if they have nothing but physical relationship. Love is not just a feeling. Love can't last for so long. It will always be a matter of choice.
If you have someone you treasure the most while you experience how it feels like to be alienated first hand, you would want nothing but to protect it in your own way and that's what Ei did all this time, especially if he is alienated in his own household in a very young age. Ei has nothing but his knowledge for ten years— he suffered a lot and it takes too much courage to continue and he doesn't want Gin to experience what he had been through. It's not that he doesn't believe in Gin's love, it's the society that he's so afraid of than the love itself.
forgive me daddy for i have sinned