Revealing the truth to her here and now would do nothing but make her hate him. She already turned him down once, revealing the deception would make her think he was toying with her and her feelings. What the MC is trying to do is be the bigger person by bowing out while he has the chance. Now he can allow her the opportunity to heal and move on, while he can set aside his guilt for constantly lying to her. And I'm like 90% sure he has no intention of using the opportunity to make a move on her. He's just trying to put a stop to the whole charade as bloodlessly as he can.