Was this a bad thing to do?

I can understand why he got upset, but I think what you did was understandable. He is in the wrong here, and if you are still together you should leave him and here is why: He obviously texted you from that other number as a way of testing you because he didnt trust you to be faithful to him and he was looking for (a) a reason to break up with you (b) a reason to fight or (c) proof that you arent trustworthy. then him saying that he prefers his ex and that you mean nothing to him make it clear that the relationship with him is unhealthy and he doesnt treat you right. He sounds like a jerk and I think you are better off without him.