Is weeping during prayer out of sadness over unfulfilled wishes considered forbidden (haram), and what should one do for their supplications to be answered in such circumstances, especially after repeated disappointments?

A servant should have a good opinion of Allah and be certain that his provision is guaranteed and decreed, and that Allah deals with him according to his expectation of Him. He should also be highly ambitious in supplication and aspirations, and not make a single job his only hope, for Allah may compensate him with something better than he aspires to, as happened to Moses (peace be upon him) when he went to fetch fire but returned as one spoken to by Allah. He should continue supplicating and not grow weary, for supplication is answered as long as it does not involve sin or severance of kinship ties, and as long as its performer does not rush and abandon the supplication. Allah Almighty grants the supplicant one of three things: He either hastens his supplication, or stores it for him in the Hereafter, or averts from him an equivalent amount of evil. Therefore, a servant should knock on every possible door and know that Allah chooses for His servants what is best for them.