Since it is a pub girl, it should be easy to stop it from
becoming a serious relationship.
Of course if he is not serious about the pub girl, and he is only
playing around, you break up this one, he goes with another one,
that's all.
The way to stop it from becoming serious is easy if you are willing
to spend some money.
As a pub girl, you can get a guy to go to the pub, buy her drinks,
give her money and play with her.
You video it and upload to u-tube.
Next you tell the jerk that you 'happen' to see a video of his pub
girl kissing another guy (or worse) in u-tube.
But like I said, if he is not serious about the pub girl, he
wouldn't be bothered at all.
If he tells the girl not to do it again, she would demand that he
supports her and waste all his money. Which is not a bad revenge at
all... 
