It depends on what the policy of a Chinese university is. Some of them don't care if you have a GF on campus but it can't be a students from any of your classes. Some of them don't want you having a GF from the same campus.

I has a post graduate GF ( 26 y/o ) when I lived in Nanning from the same campus as me. She was studying comparative literature and in a different department to me. Everyone new and nobody really cared. Some teachers there even said "congratulations".

If she had been 20 years old and one of my students though I probably would have been fired. Sleeping with your own students is usually a sackable offence.