Okay, I'll try to tie everything together. Though it could be a little loose tie.
Summer's family does not approve of her relationship with MC, but they see it as some childhood plaything and do not act on it. Then they notice it's more than that, so they try to stop them, hence the ice cream scene. Then, when they go to the cabin—MC mentioned it's not a close distance—they are trying to run away together. Nami, out of jealousy or fear of losing MC, tells their whereabouts to Summer's family. Summer's family acts on it, and send some people try to fetch Summer, but when they try, MC tries to stop them and gets heavily beaten by the henchmen. Thus he hates knights in shining armor. Sent to the hospital with heavy wounds, thus his mental condition. Summer met with MC one last time and gave him the rubber as a parting gift. She lets go of MC because she does not want him to get hurt more. After her disappearance, MC broke down, and Nami feels terrible about it and comes clean about what happened. MC forgave her because he understood why she did it, and they promised each other never to talk about it again.
Please don't dig too deep though, it's already too fragile as it is.
, but you are right, Ocean has changed the game so much, we can´t know right know which way will take the game. In my theory MC don´t know nothing about the implication of Nami, that explain the good relationship between them.
