妹纸你萌到了我的心
[mèi zhĭ nĭ méng dào le wŏ de xīn]
'Little Sister Paper, You Melonseedled my Heart'. It’s a cute and lighthearted way of saying 'You melt my heart', probably directed at younger girls. '妹纸' is internet slang for 'little sister' used affectionately online, and '萌到了' implies being overwhelmed by cuteness or sweetness.