[Stiles forces himself to slow down, taking deep breaths.]

Derek, the last time I tried to tell him about this, when the library came open, he just looked at me blankly. I love him, but he doesn't get it. And of course you know--you've helped me. [Stiles shakes his head.] Fine, I'll tell him.

I just think it's bullshit he can't get over whatever issue he has with you.