
Personally, i think it's not entirely their fault either. It is said that they did try to help him through but seems og Sihyeon was far too troubled to properly be open with them. And they're all pretty much working, in an idol industry too, so I'm sure they'd probably have been dealing with their own stuff too. I think it's just that they couldn't understand what they could do for him and only when Sihyeon was a bit willing to be around them, do they really change. This is also shown with the black haired guy being awake when sihyeon would have a breakdown after fights, the red haired also lashing out(which is def not the best way) i believe cause sihyeon wasn't opening up. I think they did care, it wasn't that they all turned their backs, i think it was just that they didn't know the correct approach and were waiting for Og sihyeon to open to them first.
The one at fault should be the ex lover who betrayed Sihyeon and what the og Sihyeon needed was definitely a professional help
Feel free to correct me tho if I'm wrong.

i'm not pointing who's at fault here, i'm just disappointed and cringing at his group. they knew sihyeon badly needed some money and what do they do? pink haired knew what's happening and what did he do? did you even remember when sihyeon fainted and the members think that sihyeon might remember something? they were ANXIOUS AND GUILTY . :))
kinda sad that his group be acting all friendly and supportive now (especially the pink-haired one, lol) towards sihyeon when they couldn't even support the og sihyeon . only people introduced to sihyeon's sister deserve his love.