It wasn't that hard to see, actually, when Stiles thought back about it now. He should have known. Should have realized what was going on a long time ago.
The first time Stiles saw fear in Derek's eyes wasn't when Stiles himself thought Derek was dying from the wound in his arm. No.
The first time Stiles saw fear in the Alpha's eyes was when he demanded Stiles to break the circle he had worked so hard to make, because he thought Scott was dying.
The first time Stiles saw sadness and rejection in the werewolf's eyes was when Scott told him he might be an Alpha, but he wasn't his.
The first time Stiles saw a genuine smile form on Derek's face, it was directed at Scott, even if Scott himself didn't see the smile, Stiles saw it all too well.
Derek would lean against a wall when they had a little group meeting, seemingly observing the group, but his eyes were always firmly locked onto Scott. Almost in quiet adoration and love, which, well…that Was a didn't see that emotion a lot, especially not in Derek's eyes. Again, Scott might be the oblivious one, but Stiles wasn't.
When someone would 'have to talk to Derek', somehow Scott was always appointed for the task. Much to Scott's surprise, but not to Stiles', Derek (almost) always caved; or at least found a better way that would make Scott feel better.
It was obvious, really. At least it was to Stiles. And to Isaac, apparently, because Isaac caught Stiles' gaze once after having studied Derek and Scott, and gave him a knowing smirk. Or maybe Isaac thought there was more meaning behind Stiles' looks to the two other wereweloves. Which…Oh no…so not going there.
So, it wasn't a surprise, really, when Stiles arrived at Scott's house one night, Melissa was on call and he still had the key of the front door, let himself in and went upstairs, ready to wake Scott up and maybe scare him a little while he was at it; only to find out that Scott wasn't alone.
There, in Scott's way too small bed, were two bodies, their limbs so entwined and tangled up that you couldn't even see where one person began and the other one stopped.
Stiles, not able to stop himself, took out his iphone and snatched a quick picture, smiling to himself. Then he closed the door and left the house again as quietly as he could.
Now he had proof that he was right.
Oh, Peter had so lost that bet.