How does one deal with the inability to marry as a divine decree, especially when it leads to satanic whispers and a feeling that Allah has withheld something He is capable of giving?

You must know that Allah is Wise and All-Aware; He places things in their rightful places, and He does not withhold anything except for the benefit of His servant. So, entrust your affairs to Him and submit to His decree and divine will. If He facilitates marriage for you, then marry. If He stands between you and it, then do not object. Ask Allah for His bounty and humble yourself before Him to facilitate marriage, for perhaps the delay is so that Allah may hear your supplication or so that you may strive in worship. Take the necessary means, entrust your affairs to Allah, and be content with His management.