Why did Gin betray aizen in bleach manga/anime?

According to the anime, Gin never liked Aizen to begin with and was always trying to find the right moment to assassinate him. gin Said that he new that Aizen was going to cause harm to those around him, especially Matsumoto, who Gin cared for very much, but he never really showed it. So Gin wanted to try and Kill Aizen when he was at his most powerful so that Aizen would never come back again. But since Aizen was practically God, that really didn't work.