Is expiation obligatory only for an oath, or is it necessary to fulfill a vow if one is unable to do so after breaking an oath to abstain from a lawful act with one's wife, given that there is a vow to pay money and fast for a month?

If someone makes a covenant with Allah concerning a permissible matter, it is an oath that requires fulfillment. If they break it, they must offer an expiation for an oath (kaffarat yamin). If they obligate themselves to fast for a month or give a certain amount in charity should they break it, this is a "vow of obstinacy" (nadhr lajaj). The person is then given a choice between fulfilling what they committed to or offering an expiation for an oath. Therefore, if someone breaks their commitment and does not wish to fulfill their vow, they owe two expiations: one for the oath and another for the vow.