[lè ér wàng fǎn]   

乐    而    忘    返    非常快乐，竟忘记回家。形容沉迷于某种场合，舍不得离开。

乐而忘返，指非常快乐，竟忘记回家。形容沉迷于某种场合，舍不得离开。

Enjoy oneself so much that one doesn't want to come back

乐不可支    乐山乐水    乐天任命    乐以忘忧    乐极生哀