He doesn't know how to comfort me?

Been best friends for at least 5 years, but we recently started dating. I had suddenly to put my dog to sleep yesterday and it practically killed me too. She was 13 years old, and my first dog. My boyfriend couldn't have been less comforting. When I told him, he said "sorry for your loss" and that was about it. I asked him to come over later but he responded by saying he had other plans, so at this point I'm high in my emotions and I broke up with him. I'm not a priority to him, but I don't understand how he could be so cold as to not even ask me if I'm okay. He was better at comforting me when we were friends.
He doesn't know how to comfort me?
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