Hmm...I'm probably going to sound like th devil's advocate here,
so let me preface this by saying that I love my Gwenny wholeheartedly and it sucks donkey balls that witchcraft made her go against her truest nature and do the things she did. BUT, I can see why no one (at this point) is questioning as to why she did it or wondering if something was rotten in Denmark yet.
As much as it brought bile to my mouth to see it, Gwen didn't just show up on the night she kissed Lance; she went to his tent, she began to look at him longingly - people were bound to have noticed. And then when Arthur found them, he didn't just see them in close quarters and then immediately charge, he watched them - mostly Gwen - to see how she was reacting. She wasn't just being kissed by Lance, she was kissing him, and showing him affection that up until then Arthur had only known. Another factor is that back then, women were easily villainized, particularly sexually.
.As for Elyan's lack of support or interaction, I do agree that he should have at least said a word to his sister when she was leaving if not visited her in the cell, but it truly wasn't that false to character for him not to. The writers have dropped a major ball on the relationship between Gwen and her brother since the beginning. We never see them spend time together or really even speak of one another, even in each other's presence. As for the other knights, I believe they were displaying the whole "bros before hoes" attitude of hurting with their King/bff.
On top of all of that, Gwen herself was acting guilty. It wasn't like other enchantments in the past where people come out of it not remembering what they did or where they were or showing some kind of obvious disorientation; Gwen's emotions were consistent with a guilty person, so it basically confirmed any doubts in most that she was fully aware of what she was doing, but just had no excuse for her behaviour. (Bugger you, Morgana!)
I think that's what made this episode one of the best (And most grown up) that Merlin's had yet. Even if it's discovered that Morgana's hand was involved in Gwen's actions, what is going to bring them back together is going to be their mutual realization that they cannot live without one another, and when they do come together they will be truly vowing to forsake all others (dead or otherwise) once they marry. We'll have our wedding; and best of all, it'll be with them both knowing that there is nothing and no one that will ever come between them.
Thoughts? Shall I duck zee tomatoes?