He has a girlfriend and has already dated for 1 month, he often spend his time with his girlfriend which is a good thing but, he left me when I was sad or angry and he doesn't even have any interest in talking to me ever since he got a girlfriend. He left his sister for his girlfriend, I really hate that kind of have a relationship and abandon your friendship. I am really very angry with him but he doesn't even know the reason. He says that he treats me as a sister but I don't get the feeling of being treasured by him as his sister, I feel like I'm being used by him, he only finds me when he is lonely. What should I do about him?