AITA for spending money my SO specifically said not to spend?

So my boyfriend never has much of an opinion about anything and has told me so many times that I should do what I want because I know what's best and he's not that fussed about anything. Tonight however he had a major opinion and is pissed off at me. <br><br>My gran passed away last week, and I am going to a family dinner tonight to celebrate her life. I asked my boyfriend if he wants to come and he said no because he's not a people person. I told him that's fine but if he changes his mind please come he'd be really welcomed. He said that's ok. He then said I don't want you to buy a new dress. I said ok, no problem. So I told my best friend what had happened and asked her if she wanted to come. She said yes and I said awesome. I asked her if she wanted to go shopping with me to get a new dress and she said no because your boyfriend said don't buy one. So I went by myself and got a really nice dress and then came home and put it on. I came through to tell my boyfriend I'm leaving and am wearing the new dress and he completely lost it at me and is calling me an AH saying I disobeyed him and am a bitch. I told him I'm not his dog and can do what I want but he said that I'm not a good girlfriend as I clearly don't obey him when he tells me what to do. <br><br>I do live with him but I'm not his dog. I feel really bad that he is upset but I seriously don't get why he cares about me wearing a new dress.