The short answer is probably his wife Antonina, who was a childhood bestie of the Empress Theodora. Theodora was a, ah, strong personality who was prone to emphatic answers to threats to her reign, which depended on her husband Emperor Justinian. For example, she ordered the imperial guard to intervene in the Nika riots by putting 30,000 unarmed spectators to the sword. You didn’t mess with Theodora...
Technically, it was Justinian who ordered the Nika revolt put down with the sword. But Theodora definitely put the steel in his spine. I think that if Belisarius had taken the Western throne, an outcome where he ends up dead in a pool of blood thanks to an assassin commissioned by Theodora is not out of the question.