One of my favorite hobby horses—getting “whom” correct.
Subordinate clauses are stumbling blocks for a lot of people because these clauses often put the direct object first, where the subject usually goes. So the nominative form, “who” gets used, even though the actual subject is “you.”
Whenever you have a who/whom decision to make, first decide what is the verb, then look for the subject. Then decide whether the “who” word is the subject or the object. “Who” is a subject, “whom” is an object.