About Wend...the character has many many bad traits and her relationship with Stan has always been problematic just like it was likable for the audience at the beginning. The problem with Wendy is that she has been used to show an imagine of women is a bother for most part of the audience. Wendy is almost something Stan has to endure, they break up all the time and it feels like she simply doesn't love him at all.
And while her romantic relationship with Stan is popular among a part of the fandom her history has created the conflict where some people make of her a villain and some others simply used her to romanticize Stan and Kyle's friendship. The typical "he isn't happy in his relationship with a girl, he would be happy in a gay relationship" thing