我不懂那个本来简单的你
[wŏ bù dŏng nèi gè bĕn lái jiăn dān de nĭ]
'I Don't Understand That Formerly Simple You' implies that over time or due to some events, someone close has changed greatly making them hard to understand now. There's a tone of regret or sadness in reminiscing about a simpler, more genuine past version of that person.