对你微笑纯属礼貌为你而哭纯属在乎
[duì nĭ wēi xiào chún shŭ lĭ mào wéi nĭ ér kū chún shŭ zài hū]
It means 'I smile at you only out of politeness and I cry for you just because I care about you.' The former phrase implies that the feelings toward someone are not genuine while the latter expresses sincere concern.