Aaargh!!
LeHah: How dare you insult the name of one of the finest generals in history!?
Also there were two Byzantine emperors by name of Justin and neither of them were particularly admirable.
Earthworm: Damn straight!
Quarto: Belisarius was by no means the cause of the end of the Byzantine Empire. If you're going to blame someone you should blame Justinian I. He's the one who went and ordered the invasion of North Africa and Italy. It was his dream to recreate the old Roman Empire. Belisarius was a general who temporarily earned the emperor's trust. In one year he more or less conquered the old Roman province in modern day Tunisia. Over the next couple of years he made plenty of progress in Italy.
The reason these campaigns drained the empire's fiscal reserves include the following:
A) Justinian overspent on massive building programmes, including the Hagia Sophia Church. Obviously Belisarius had no say in this.
B) Justinian insisted on invading people who were not an immediate threat to the Byzantine Empire. When it came to dealing with people who were a threat to the empire he preferred to bribe them to go away. Again Belisarius had nothing to do with that.
C) Justinian was no general. He didn't have a problem with fighting on multiple fronts. Multiple wars obviously place a burden on the treasury.
D) Justinian didn't trust Belisarius. Resultantly he shuttled that general between Italy and Syria, thus preventing Belisarius from getting anything done.
E) Justinian insisted on constantly dividing the military commands between different generals. Consequentially no other general was able to achieve lasting success. Hence the wars dragged on.
Finally the Byzantine Empire lasted to the year 1453. Justinian and Belisarius died in 565. That's an 888 year difference. Neither man is truly too blame for the empire's final collapse. However Justinian's policies definitely contributed to the disasters of the seventh century. Again though the incompetence of certain emperors that succeeded Justinian had a greater impact on those disasters than Justinian.