How can I learn to love Allah the Almighty, and will His love compensate for the emptiness resulting from my attachment to a girl, and should I be content with His love alone?

The first steps to treating what you mentioned are acknowledging your mistake and seeking a remedy for it. Attaining good and escaping evil begins by turning to Allah Almighty, supplicating to Him, and imploring Him. Increase your recitation of the Prophetic supplication: "O Allah, I ask You for the doing of good deeds, the abandoning of evil deeds, and the love of the poor and needy. And that You forgive me and have mercy on me. And if You intend a trial for a people, then take my soul without me being tried. I ask You for Your love, the love of those who love You, and the love of a deed that brings me closer to Your love."