蓦然回首我爱过好多狗
[mò rán huí shŏu wŏ ài guò hăo duō gŏu]
Literally, it means 'I suddenly looked back and realized I have loved many dogs.' In modern internet slang terms, 'dog' can represent disloyalty. So this may express that when recalling past relationships or experiences, he/she has encountered various betrayals or deceitful behaviors.