What is the expiation for an oath sworn by someone who swore not to eat a single bite with his companions due to disagreements between them?

If you have not yet broken your oath, it is better to uphold it, based on the Almighty's saying: "And guard your oaths" (Qur'an 5:89). This means that you should not break your oath out of reverence for the name of Allah, unless the oath was to abandon a recommended act or to commit a disliked act. In such a case, it is better to break your oath and offer expiation. Eating with companions when there are disagreements is not a recommended act, unless it brings about affection and resolves the disagreement. In that case, you must eat with them and expiate your oath. The expiation for an oath is feeding ten poor persons, or clothing them, or freeing a slave. And whoever cannot find means, then fasting for three days.