The first thing I have to say is this: I love Kurt. I love Blaine. I love Kurt and Blaine together. I think they're perfect for each other. I am a Klaine shipper all the way.
I also love angst.
Sebastian is cocky, confident, and talented. And he know it. He is obviously used to getting what he wants. He wants Blaine. I think that this is a good opportunity for Kurt and Blaine to grow as a couple. Sure, the road will be bumpy, and there will be a lot of hurt. But it will be for them in the long run. This is why I like Sebastian.
It doesn't hurt that Grant Gustin is really hot, either.