Я начинаю понимать, почему вы с Адамом так близки.

The intended meaning in English: "... why you{singular} and Adam are so close"

The speaker and her interlocutor are on close enough terms to call each other by "ты", which rules out the possibility of her suddenly switching to the polite, singular "вы".

On the other hand, the context also makes it abundantly clear that her interlocutor is the only person here that she is referring to as having a close relationship with Adam, so it seems logical to discard the inexplicably plural "вы" in favour of the casual, singular "ты":

Я начинаю понимать, почему ты с Адамом так близок.

This apparent idiosyncrasy -- using the plural "вы (с Адамом)" when, in fact, the casual, singular "ты (с Адамом)" is obviously implied -- throws me off here.

What is the rationale behind this construction?

Я начинаю понимать, почему вы с Адамом так близки.

The intended meaning: "you{singular, her interlocutor} and Adam are so close"

The speaker and her interlocutor are on close enough terms to call each other by "ты", which rules out the possibility of her suddenly switching to the polite, singular "вы".

On the other hand, the context also makes it abundantly clear that her interlocutor is the only person here that she is referring to as having a close relationship with Adam, so it seems logical to discard the inexplicably plural "вы" in favour of the casual, singular "ты":

Я начинаю понимать, почему ты с Адамом так близок.

This apparent idiosyncrasy -- using the plural "вы (с Адамом)" when, in fact, the casual, singular "ты (с Адамом)" is obviously implied -- throws me off here. What is the rationale behind this?

Я начинаю понимать, почему вы с Адамом так близки.

The speaker and her interlocutor are on close enough terms to call each other by "ты", which rules out the possibility of her suddenly switching to the polite, singular "вы".

On the other hand, the context also makes it abundantly clear that her interlocutor is the only person here that she is referring to as having a close relationship with Adam, so it seems logical to discard the inexplicably plural "вы" in favour of the casual, singular "ты":

Я начинаю понимать, почему ты с Адамом так близок.

This apparent idiosyncrasy -- using the plural "вы (с Адамом)" when, in fact, the casual, singular "ты (с Адамом)" is obviously implied -- throws me off here.

What is the rationale behind this construction?

Я начинаю понимать, почему вы с Адамом так близки.

The intended meaning in English: "... why you{singular} and Adam are so close"

The speaker and her interlocutor are on close enough terms to call each other by "ты", which rules out the possibility of her suddenly switching to the polite, singular "вы".

On the other hand, the context also makes it abundantly clear that her interlocutor is the only person here that she is referring to as having a close relationship with Adam, so it seems logical to discard the inexplicably plural "вы" in favour of the casual, singular "ты":

Я начинаю понимать, почему ты с Адамом так близок.

This apparent idiosyncrasy -- using the plural "вы (с Адамом)" when, in fact, the casual, singular "ты (с Адамом)" is obviously implied -- throws me off here.

What is the rationale behind this construction?