Must one fulfill a vow to marry a second woman to protect a girl if the condition upon which it was contingent is met, or is expiation obligatory, given the hesitation regarding the marriage for reasons that are not strong?

Scholars have differed on the ruling of marrying a second wife, oscillating between preferring it (istihbab) and permitting it (ibahah). Most of them have favored the view that limiting oneself to one wife is better. Vowing to marry a second wife is considered a vow concerning a permissible act, and it is not binding according to many scholars. Those who hold it to be binding believe that the person who made the vow has the choice between fulfilling it or paying an expiation for breaking an oath (kaffarat yamin). Based on this, you are not obligated to marry a second wife. If you do marry her, there is no harm. However, if you choose not to marry her, it is more cautious to pay an expiation for breaking an oath.