Is it permissible to agree to marry after having made a vow to abandon marriage for the sake of Allah? And in this case, would the marriage be unlawful or unblessed?

Your vow to abstain from marriage is closer to a vow of disobedience, because it is an abandonment of the Sunnah of the Prophet, peace and blessings be upon him, who said: "Whoever turns away from my Sunnah is not of me." And his Sunnah regarding marriage is a path to chastity and protection. A vow of disobedience is not permissible to fulfill, due to his saying, peace and blessings be upon him: "Whoever vows to disobey Allah, let him not disobey Him."