Han and Leia's son, Ben, was Luke's padawan. Ben then betrayed Luke, turned to the dark side, and took the name Kylo Ren—just like his grandfather, Darth Vader. He even made a Vader-esque facemask—which in the opening moments of The Force Awakens, Poe Dameron calls an "apparatus" and says, mockingly, that "it's hard to understand [him.]" In the trailer for The Last Jedi, Kylo Ren's precious apparatus is seen briefly, and it looks like it was smashed and discarded.
It's unlikely that this means Ren has renounced the dark side and returned to his mother and the Resistance. So what could it mean? If he is losing what little light is still left in him to the dark side, will he become deformed like Darth Sidious?
Whatever happens to Kylo Ren, there's a good chance that Luke blames himself for losing his apprentice to the dark side, and it's possible that Ren's betrayal soured him to the whole idea of the Force. That may be why he's ready for the Jedi to end. You don't grow a beard that majestic and then run off to live in solitude if your conscience is completely clean. You stick around, so you can mind-trick people into complimenting your beard while you're hanging out between galactic crises. Every Jedi worth their midichlorian count knows that.
You can't escape the M-word. It's canon, people.