Yes Glee has been known for rushing things. Sometimes it works out for the better. But the majority of the time,yeah not so much. But as a loyal fan I love every minute of it :) Even if I see it's flaws.

Blaine does have that problem of being clueless to important things that are going on around him. First with Kurt and now with Sebastian being the enemy/homewrecker! And bless Blaine's wonderful heart in believeig the best in people, always thinking others have good intentions. He should have learned his lesson when dealing with Finn and Santana.
Yes I agree with you that Sebastian is taking advantage of the fact that Blaine is friends with the Warblers and doesn't think of them as competition or that they'll do anything unsavory for the sake of winning. And with that clip that we saw I hope he'll learn that lesson.

I also liked Sebastians character from the beginning too. Granted I wasn't too thrilled that there was gonna be someone that might disturbe the peace with Blaine and Kurt. Then when I saw the jealousy and posessiveness that it brought out in Kurt I just couldn't really hate Sebastian. I like that he's stirring the pot with those two.

I can't wait for the 'Michael' episode so that everyone (especially Blaine) will see Sebastian's true colors! It's going to be awesome.