I feel like he just wants a relationship and some affection.
Jooin loves Yawhi sincerely but he always feels like Yawhi can't return those feelings or Yawhi never liked him in the first place. You can see he is very happy when Yawhi treated him better, but he feels Yawhi is ashamed of their relationship as he does not show affection outside at all. Only in the bed, he wanted to keep believing Yawhi just doesn't know how to show affection. He has been enduring so long so he was tired of their relationship. He slipped his tongue and said he wants to end it even though he doesn't want to really end it, but when Yawhi said the words Jooin wanted to hear, Jooin was happy in the moment but when he really sees Yawhi. He knew Yawhi said that without affection, nervousness or other emotions, he knew he had to end it and does not want to be trapped in his own fantasy anymore. But this break up will make Yawhi's character development.
So...what exactly is it that he wants? A whole chapter to talk and nothing was explained