你是我心头的一根刺
[nĭ shì wŏ xīn tóu de yī gēn cì]
'You are a thorn in my heart' directly conveys the mixed emotions towards someone who causes constant annoyance, pain yet might also have unexpressed affection. The metaphor illustrates this person stays deeply planted in the speaker's heart just as how a thorn can prick sharply even though it remains unseen.