She was right about one thing: there was a part of him, deep down, that wanted to try it for reasons that extended beyond the dozens that he constantly reminded Ruby of. He was doing it because he cared about other people, because it was the only way to keep them safe, because he didn't want to see anyone get hurt. Those were the instant shots that he fired out when the discussion came up, but they were all bullets in the gun of excuses that Sam had loaded. All different, but not every last one of them landing on a note that Sam felt to be a somewhat noble one.
Noble people who put themselves in morally questionably situations like this one didn't do it because they wanted to know how it would make them feel afterward. Sam was torn as far as all of that went. Having power, being able to have more. Who wouldn't have been tempted by the knowledge of such a thing? No less having it shoved right under their noses? It was a driving force, right along with the others that he carried. Yet it remained the quiet one. He'd never admit it to anyone out there. Not Ruby and certainly not himself. But it was an existing factor. One that would grow louder. Stronger.
But not right now. Now, Sam's heart was in it for the right reasons.
He took her wrist with a shaking hand. He couldn't help it. Sam was scared of all of this. Curious and determined, but very much terrified. Having already gotten her permission to proceed, he shifted a little in place, taking in the sight of the red substance that was pouring out from the fresh wound before him. She was a demon and she had probably felt a lot worse, but Sam found himself being very careful with the way that he was handling her arm. She was bleeding. Ruby was already injured. He didn't need to add on to whatever it was that she felt from the result of her actions. In order to aid him.
Taking an unsteady breath, Sam slowly began to lean forward. He came up to her wrist, maybe a few inches from it, before he paused. Hesitation, doubts, fear. All stopping him. He could see the disapproving look from his Dad, the furious glare from Dean, the disappointed expression from his mother...
They all dissappeared the second he closed his mouth around her wrist, the unpleasantly sharp taste of her blood filling his mouth; metal and...and...was that sulfur? Nose wrinkling in disgust, Sam gripped at her wrist a bit more tightly, doing his best to take control of his senses. It was different from before. There was a lot more blood to take in. This was harder for him to adjust to. It wasn't a little sliver of blood, it was a lot and he was doing everything in his power to keep himself from gagging.
Keep drinking, he urged himself, screwing his eyes shut as that unpleasant feeling riled it's way through the pit of his stomach.