So I've been thinking, and I think one of the reasons I'm not interested in reading X-Men First Class fic unless it 1.) is AU, or 2.) involves Raven (or at least Emma) in some capacity, no matter how minor a role, is because Erik and Charles fundamentally bore me. Or at least, Erik and Charles as fandom most commonly chooses to portray them bore me.
I like the way a lot of AUs paint their relationship, because the AUs really push to redefine the relationship between the two, whether it's an AU where there is no "divorce", or a completely different AU in a completely different universe (those are always just fun because they're fun, though).
But the idea of a universe where Erik and Charles part ways on that beach in Cuba, and Charles spends more time/effort/heart mourning the end of his epic romance with Erik instead of mourning the fact that the sister he grew up with has chosen to leave him behind to perpetrate genocide -- that is upsetting to me. I may not ship Erik/Charles in that fanfic that solely focuses on Erik/Charles sappy romances or porn with no plot will bore me, but I do ship Erik/Charles in that I see their epic romance, I acknowledge it, and the idea of a non-Erik/Charles relationship is bizarre to me and must be pulled off really well before I buy it.
Given all that, I still don't buy that Charles's epic romance with Erik is more important than his kinship with Raven, who is for all intents and purposes his sister. I will never understand any proposed situation in which a character would choose his/her love over his/her family (provided the family in question isn't composed of horrible people, or unaccepting people, or any other number of factors that would make it imminently reasonable for love>family).