I really dislike the way they're handling their friendship this season... but the way Mercedes didn't really object to what Kurt said (the substituting for a boyfriend thing) made me think he may have been kinda... right about it? I mean, Mercedes fell for Kurt at the beginning of S1. Sure, she now knows that Kurt is gay, but the feelings may still be there. I mean, I really don't like the implications of that, that girls can't be just friends with guys (without any attraction/romantic feelings involved), but this stuff does happen in real life in friendships between hetero women and gay men. I hated the way that confrontation was handled though, Kurt's "I'm not breaking it off with Blaine" seemed to come out of nowhere and it felt like we missed some scenes before it. And he was really insensitive about the whole thing.
I also didn't like how he tried to hook her up with that guy and kept breaking up their plans because of Blaine. I guess it's yet another example of Kurt showing us that love makes you stupid. I can kinda understand him though, he's waited his whole life to meet someone like Blaine. Still, he should have remembered who his best friend is.