What does Romeo mean when he says, "Oh, dear account! My life is my foe's debt"?

Shakespeare is using a metaphor here wherein Romeo compares his meeting and falling in love with Juliet to a ledger, or a record of debts and payments. As my colleague stated, Romeo has just learned Juliet's identity. She is a Capulet, his families sworn enemy. So, when he says, "Oh dear account! My life is my foe's debt," what he means is that he is forever in debt to his enemy for bringing him his love, Juliet. The account is dear in two ways. Juliet is dear to him. Also, the debt is dear, meaning very costly; he fears his enemy Capulet will not accept his "payment" of love and gratitude--that Capulet will keep him from his dear Juliet.

When Romeo discovers that the girl he loves is a member of theenemies family, he knows that he is as good as dead if anyone finds out. To saymy life is my foe's debt is kind of like saying my enemy owes it to himself (and the rest of his family) to kill me. Killing Romeo would seem justifiable to the Capulets because they hated his family and certainly hated the idea of any union between their families