How does a young man rectify his intention in marrying a committed girl whom he loves and promised to marry, so that it becomes an act of obedience to God and chastity for the soul, not merely for love, in order to attain reward from God?

A good intention transforms ordinary acts into acts of worship. Rectifying an intention does not require speech or action; rather, it is sufficient to intend the act for the sake of Allah. So, whoever intends by his marriage to a religious woman to obey the command of the Prophet, peace and blessings be upon him, to follow his Sunnah, to protect himself and his wife from sin, and to build a Muslim household, he will be rewarded and appreciated. Allah the Almighty said: "Whoever desires the harvest of the Hereafter - We increase for him in his harvest." And the Prophet, peace and blessings be upon him, said: "A woman is married for four things: for her wealth, for her lineage, for her beauty, or for her religiosity. So, choose the religious woman, and you will prosper."