себе, reflexive pronoun, refers to the previous defined subject/object, and so here is ты. And so it is the you of the first line, себе being dative form in this case. самому is like very or self (m. dative form), and so "С кем себе самому изменял" is like "with whom you were betraying your very self". (or simply 'your self') But not posed as question. As statement.