If you really a welwisher of your father then you have to make him realize how big mistake he done, otherwise he will keep doing with others too.
But definitely not in this way, console your boyfriend that talking to father in this issue will not change anything, may be situations become worse and you may feel more guilt to embrssing your father. Tell your bf that he want to sooth her or make her condition worse.
Promise him to communicate your father his mistake appropriately.
Next Steps
Also communicate your father about his mistake by using your mother's help because if you will not do so then he may abuse any other Innocent girl. only you can prevent.