好马不吃回头草

hǎo mǎ bù chī huí tóu cǎohaomabuchihuitoucao

1. lit. a good horse doesn't turn around and graze the same patch again (idiom)
2. fig. once you've moved on, don't go back again (romantic relationship, job etc)
3. leave the past behind

Study it in Yanamino