Same bro same
Hum from what I understood:
MC transmigrated as an imperial Prince but he didn't realized that he was in a novel at first. At some point, he met ML as a child and both got really close. Unfortunately they were later separated. Because MC was hiding his true identity at the time and ML discovered his true identity and changed to it afterward, they couldn't find each other despite both trying very hard.
In the end MC won the throne battle and became the Emperor and ML joined the rebel because he wanted to find his "big brother" who he only though was an official. Unfortunately both realized the truth way too late and MC choose to kill himself, to ML despair.
Currently MC regressed back and decided to not work so hard and avoid the throne since now he knows ML is the original protagonist but somehow ML met him earlier this time.
The reason they didn't recognize each other in the 1st transmigration was because ML was still a small child when they got separated and later a big adult. As for MC he said he was beefier and stronger in the 1st time because he worked really hard for the people and changed a lot after he got separated with ML. But in this 2nd time, since MC decided to be lazier about stuff, he physically didn't changed that much from when he was an adolescent and met ML.
I know my summary can be a bit weird so ask any question I'll try my best, though I don't know much XD
Personally I suspect ML to have also regressed the 2nd time but I don't have proof yet
Also. MC only realize he was in a book after hearing ML new identity name. But as a child ML name was different so MC had no way to recognize it. Nor to guess that ML was the protag when he heard the name later until ML asked about MC's fake identity whereabout during the rebelion
Guys I’m so fucking lost. Plz help me with this plot cause WTF???