Is expiation (kaffara) obligatory for one who swore on the Qur’an not to associate with a group of girls, fearing her father, and then violated the oath?

As long as you were not coerced into making the oath, then expiation for an oath becomes obligatory upon you if you violate your oath by associating with those girls. This expiation is: feeding ten poor persons or clothing them. If you cannot find [the means to do] that, then fasting three days.