Well it's good to be honest but I don't think what he said was that bad. He wanted to get more serious and you rejected him. Having been on that side it's really no fun and he is probably wondering why you kept seeing him and spending the night with him for two months if you didn't really like him.
Sorry, accusing someone of "having someone else" just because they don't want a serious relationship with you is childish. I could see not wanting contact anymore, but being all "I know there is someone else, and when you change your mind, don't come crawling back to me!" is just childish and douchy, and I am betting was accompanied by a foot stomp.
It was two months of dating where they rarely saw each other. It's not like they were a year in and she was saying, "I don't want a serious relationship."