(Fatwa: 1552/1469=D /1429)
You should do istikhara again for marrying the boy mentioned above; also consult the Mufti sahib mentioned in the question. If it appears good to tie the knot in view of Istikhara and consultation, then you should marry in order to get chastity with your consent of your parents. You have to give expiation for your swearing of not marrying, and you have to pay it after you will marry him when your swearing will be broken because of marriage with him. The expiation for swearing is to feed ten poor people two times to their hearts content, or give 1.633 kg wheat to ten poor or ten sewn clothes to ten poor people.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband