Friendship
They did everything together. They'd have Superhero Movie Marathon Weekends, text each other at the most inappropriate time the most randomest things that came to mind. It was a nice, easy going friendship.
But he wasn't satisfied.
He wanted Sam; Hell, he needed Sam. Blaine was 74% certain Sam knew his feelings. How could he not? Blaine wasn't exactly subtle.
While he never made any sign of returning Blaine's feelings, Blaine hadn't given up hope.
Their friendship may be great, but he wanted more.