I was curious as to their expressions. The problem is, they don't have all of the information available to them... though it might be interesting if Claudia actually asks. Jin wouldn't. But Claudia... she seems grounded enough that she might take such a course of action.
What can we say? Sparkle brings out the worse in people. Case in point: The Magical Girl Class (note how without Sparkle they start calming down and becoming... people?)
It's nice that some of the others are offering to help. You almost get the sense they can tell he's being drawn into the black hole that is Sparkle's manipulative grasp, and don't want to lose another one.
My headcanon at this point is that dan's friends loathe her just as much as normal but they tolerate her for his sake, and several people have already pointed out that she's a huge bitch and he replies "you guys are just jealous that I'm dating the prettiest girl in school" -Jin is the only one who is sticking with it.