This is very common. In a nutshell....
Alot of Thai working girls have a Farang "boyfriend". He most likely knows about her job as they met while he was a customer (this is always how it starts)
The "boyfriend" is an old bald fat Farang who is just a walking ATM machine for her. She most likely has a real Thai BF/Husband back in Isaan/Thailand and a few kids/family members she is sending money back to...