Learn Hardcore Russian: Я скучаю по друзьям, когда уезжаю из города.

In Russian, скучать (“to miss,” literally “to be bored for”) is always followed by по plus the dative case. You cannot say скучать друзей or скучать друзей without по. So скучать по друзьям literally means “to miss (feel longing for) friends.”

Why is друзьям in the dative plural, not accusative or something else?

Because after по with verbs of longing (скучать, тосковать) the noun takes dative. Here friends are plural, so друзья → друзьям (dative plural).

Why is уезжаю imperfective present (“I leave”) instead of perfective future (“I will leave”)?

In subordinate time clauses introduced by когда, Russian normally uses the imperfective present form even if you mean “when I will leave.” So когда уезжаю из города can express a future event in that “when I leave the city…”

What’s the difference between ездить/ездить, ехать, уезжать, and уехать here? Why уезжаю?

Ехать (imperfective, unidirectional) = “to be going by transport now.”
Ездить (imperfective, multidirectional or habitual) = “to go by transport regularly or back and forth.”
Уезжать (imperfective) = “to depart, to leave (by transport).”
Уехать (perfective) = “to depart/leave” (completed action).
Here you want the ongoing action (“whenever I go away from the city”), so you choose the imperfective уезжаю.

Why is it из города (genitive) after уезжаю?

The preposition из meaning “out of” always takes the genitive case. Город in genitive becomes города. So из города = “out of (the) city.”

Why is there a comma before когда?

Because когда introduces a subordinate clause of time (“when I leave…”). In Russian punctuation, you separate the main clause from the subordinate clause with a comma.

Why is there no я before уезжаю?

Russian often drops subject pronouns when the verb ending clearly indicates person and number. Уезжаю ends in –ю, so we know it’s first person singular (“I leave”). Adding я again is not wrong, but it’s redundant and less natural.

Could you use a different verb like тосковать instead of скучать? What’s the nuance?

Yes, тосковать по друзьям is possible, but it’s more literary or poetic and implies deeper, more melancholy longing. Скучать is the everyday word for “to miss someone.”