Your teacher's point is correct. Records of marriage existed in ancient China for eunuchs. The earliest can be traced back to the Han Dynasty. Unlike ordinary people, eunuchs lost their ability to have children. But they still wanted to receive care from the opposite sex inside. So there was a surge of marriages in the Ming Dynasty, where eunuchs were strong. Some ming dynasty eunuchs and maidens took the initiative to form a special marriage relationship. They would take care of each other in the palace and become spiritual rather than physical companions. 

I remember reading somewhere that working in the palace was considered a very good job, even if it did mean you had to get your bits chopped off.

Imagine coming home one day and having your parents proudly tell you they'd found you a great job - much better than farming corn or burying plague victims like your brothers but there are a few small things you need to do to make it offical.

"No worries Dad, what do they need? Notarized and stamped birth certificate? 3 character references?"

"Err...yeah, and one other minor thing... (cough, ahem) they need to hold you down while someone hacks your balls off with a knife.... but you get free lunches and you should see some of the hot girls they have working there... oh, ... "