Everyone was confused until vol.3 when we get a flashback arc which pretty much bridges IR and CoTA.
Woah... no. He got angry at her by the end of IR because she had brought his brother into Chaos and his brother ended up possessed by Caladbolg. However, 2 years later he found out she had still been taking care of him (MC) and he sought her to mend their relationship. They got closer, probably even got laid and maybe even got married. The problem is we only know about up to the time in which he became King, and then the flashback ends. Then, we also have that scene with Serin (MCs girl) stabbing him in the back during the Magnanix - which is what seems what ended up breaking their relationship completely, and what made his turning point into the cold man he's today.
As for the new kid, the authors keep saying Jae Hyuk/Nex still is the MC.