Sun was visiting Moon in one of the cells that Moon was in. You were there with Sun at his side as he and Moon talked. Sun's disappointment could be seen, but it was due to the increasing darkness caused by the Sun and Moon's conversation.

Sun and you were being threatened by Moon to kill Jack, and things were getting out of hand. So Sun talks to the computer to shock Moon if he tries to get out and do it until Moon is unconscious. After that, you and Sun started to leave the room while Sun soft spoke to himself

Sun: "He's not my brother anymore..."

The sadness in Sun's voice was there without a second thought. You heard Moon say something dark to himself as well as you walked away even more from the cells but you couldn't hear what Moon said. Everything was falling apart now ever since Solar's and other things happened

Moon: "I really hate it here. Maybe the Solar that is not mine will talk crap to me in my head."