Disclaimer: I don't own any boy bands.
Kendall will sacrifice almost anything for his dreams, for his friends' dreams; he left his home, his hockey team, his dignity back in Minnesota. He works until he can't see straight learning new songs, practicing new routines, impressing new executives. He wears black and pretends to bad; he changes himself, hoping he doesn't lose himself.
He's even willing to "date" some crazy bitch named after a car, to carry her shit, to fan her, to listen to her abuse. He's willing to participate in her farce, to be some nameless boyfriend.
But Kendall won't let her have Logan, won't let Logan be trapped. Not Logan, who couldn't sing or dance, who put becoming a doctor on hold indefinitely. Logan won't lose his soul to some Hollywood harpy. Kendall can't bear losing Logan: that would be losing himself.