My 14 year old daugher's boyfriend is cheating on her, what should I do

Anything you can do to make her aware of the situation without it becoming a polarizing issue between you and your daughter. Asking her what she thinks she should do will work better than your telling her. If your daughter is like many teenagers, mom inserting herself into it in a command and control mode will drive her in the opposite direction. Try to help her understand that what people say and what they do can be very different, a hard lesson but she's better off to learn it at 14 than 34.

Nothing. She's 14, not married to him. She has to learn to deal with Lads at some point.
Better now, than when she's 22, and pregnant from someone who might be around for the long haul.