Is the questioner's not marrying yet—despite his attempts and proposals to many girls—due to his destiny, or the word he uttered in a moment of anger: "By God, I will not find her"?

It is not possible to determine with certainty the reason for lack of success in marriage, but it unfolds according to Allah's decrees. The servant must review themselves and repent to Allah, for sins are a cause of tribulation, as stated in the Hadith Qudsi: "O My servants, it is but your deeds that I record for you, and then give you their recompense. So he who finds good, let him praise Allah, and he who finds other than that, let him blame no one but himself." Repentance, good deeds, remembrance (dhikr), supplication (du'a), and having a good opinion of Allah facilitate matters, for "And whoever fears Allah - He will make for him ease in his affair."