Meh, this bugged me for like a second but it’s pretty obvious it was just there for comedy and to segway into Brittany’s stork speech, thus informing Will that none of the kids knew anything about sex so then he could bring Holly in and “Sexy” could have a plot. It made the most sense for Brittany to confide in Santana, and in order for the plot to work Santana had to tell someone else so that it could get around and Brit could talk about the stork. No big deal imo.
No big deal for the Glee writers to further destroy Santana’s character for some episodic plot point? So. Surprising. The breaking of her trust seemed especially disgusting to me because of how naive and innocent Brittany really is, in some ways, and if pregnant could have really used the support of a trustworthy friend.
BUT, as we saw after, Santana’s head over heels for her and if in that moment she was too shell-shocked to offer support herself, at least she let the nicest of their friends know so they could be there. Plus, the part of me that rejoices in Santana’s evil side thought that she might have been hoping to break them up, considering the “don’t tell Artie” thing.