Yeah, he really sort of stumbled into it all and kind of tries his best to be a good s/o to Hyunjin while also attempting to befriend the others. MinBin were easy, but he's much in the same boat as Changbin when it comes to Jisung - hence why they're good friends.
He's okay with Hyunjin's feelings for Jisung because Hyunjin treats Sung like a best friend and no more, and has never given the impression that he wanted to be more either. Besides, everyone in the little family of four seems a little more closely tied together than friends usually are, so Chan just sort of goes with the flow of them and tries his best to fit in. Hyunjin also ventures into his side of the social circle and tries his best to get to know him better, even if NFR didn't touch on it, so it's not like he's only giving and getting nothing in return.
Chan won't get tired of dealing with Hyunjin's friendgroup because he doesn't consider it 'dealing with' so much as just 'getting to know'. In the future, as Jisung mellows out and opens up more once he starts properly dating Felix and having had plenty therapy, things will also grow less tense because everyone else will be able to relax and stop being afraid of what might be wrong with him.

That aside, thank you so much for reading my little fics and asking me questions about them, I'm always happy to talk about my stories! 😊💕