I mean.... considering their relationship, what they've been through separately and together.... I can't say I don't understand why Khun only ever really cares about Bam...

But then again, it's not like he cares about nothing but Bam. Maybe he did at first, but being with Bam and seeing the ever caring man definitely changed him. He started caring more about his - well, their - companions. Bam changed him for the better.

And it does go both ways. Bam changed for the better because of Khun. He slowly learned to value himself more, to understand that he deserves just as much as other people. Khun made him realise that it's okay to be selfish, that it's not wrong to want things.