What is the way to heal an ailing heart and return to God after becoming extremely attached to someone who let me down?

We advise you to move past this matter and not dwell on it. Instead, attach your heart to Allah Almighty, knowing that all good is in His hands, and that there is none who can withhold the mercy He extends, nor send forth what He withholds. And that none can remove harm but Him, nor repel His grace if He intends good for you.

Turn to Allah Almighty, striving diligently in His worship, seeking His pleasure alone, relying on Him alone, and seeking assistance from Him alone, with no partner to Him.

Adopt the means of purifying the heart: contemplating the names and attributes of Allah, reflecting on death and what comes after it, on Paradise and Hell, pondering the Quran and reciting it frequently, adhering to the remembrance of Allah Almighty, striving earnestly in supplication to Him, associating with the righteous, attending gatherings of knowledge and remembrance, visiting the sick, and following funeral processions.