He might not be able to differentiate but as I have been saying this isn't about what Sam is feeling in the story and more of an outside perspective of the audience and of the writer writing this story. In the story he maybe can't differentiate but we can.
The deceit thing has nothing to do with Dylan. The deceit I refer to is him acting all good Infront of Sophia and talking all about how hot she physically is behind her back. Bringing alcohol when she didn't ask for it, continuously acting as helpless kid Infront of her to gain sympathy and move forward. As a guy to another guy do you actually buy those lines of him being unable to sleep at night and continuously having dreams about her and whatever else he said during that time just because he saw her dressed in her bra. Him trying to push the guilt onto Sophia for standing in her own balcony and even though most of the times it is him who is peeping on her.
You talk about a fantasy scenario stating that maybe he is talking like that to get through to Dylan and actually does not feel that way whereas L&P has never hinted at anything like that. It was clear and simple when we got to see Sam's actual thoughts which he can never reveal to Sophia as he talked to Dylan. Infact in the pool scene with Amber Sam emphasized on physical contact with Sophia to show Dylan up, with your explanation there was no need for him to do that at the pool, Dylan already has acknowledged Sophia's beauty, so there was no need to behave like that, even if he did he didn't have to emphasize on it Infront of dylan knowing full well that it is pissing him off.
The terms he used would trigger a son far more than if he whole heartedly said that he feels he is love with his mother. This statement could be taken casually by Dylan. Not statements like "her ass looks tasty" or whatever other things he said.