Plenty of times Sam's felt shame for his part in the chaos and discontentment experienced by his brother, and having struggled so thoroughly in his own right, he makes no excuses for himself anymore (even if Dean makes excuses for him). Undoubtedly, there's a side of Dean, and consequently (as well as in addition to) Sam, that stops short of the appropriate due diligence when involving matters of the heart. Perhaps it's fortunate Geralt doesn't struggle in the same way — impressive, if nothing else.

"Dean handles himself," he explains, "and I've learned to respect that." In part. "But none of us are without influence. Or being influenced. 'A body at rest remains at rest unless an outside force acts upon it,'" Sam quotes, although he's fallen very far from the tree where Newton postulated such things (and never mind that Geralt doesn't know Newton from Adam [another "common knowledge" item which also presents as an Earthly thing perhaps entirely lacking in context]).

"I wouldn't be much of a brother if I hadn't considered it." It's almost presented unabashedly, although Sam has the good sense to lower his gaze in time with reaching out to twist one of the books around on the table so he can investigate the cover. The fact that he feels shy of what he says doesn't make it true, and despite his efforts otherwise, Sam expects to always struggle with the thought, at least in some manner. Dean will always be the better brother, but that doesn't mean Sam stops trying.