Actually, your problem is not a problem. There is no need to be too nervous or too concerned. Perhaps, you don't have many friends, and you regard this friend you mentioned as your very good friend.
Sometimes we feel that others are happy, and we also feel happy, and we pay special attention to others' views and attitudes towards ourselves and regard others as our center, so every move of others has become the benchmark of our own happiness or depression.
Sometimes, we are self-centered, and always feel that everything in others can't affect our thoughts or actions, don't care about others' feelings, don't understand others' practices, and even don't care about others' care and love at all ... (Your friend may be such a person)
Many people around you look at you like this because you regard him as your best friend and he doesn't regard you as his best friend. In fact, all this is normal. As a person, today and tomorrow may be completely different, so you don't have to take your friends' behaviors and practices as a yardstick for your happiness. Make as many friends as possible, communicate with your family as much as possible, and make as many male and female friends as possible (if the age is right)! In short, don't give your body and mind to others to control, but learn to control yourself appropriately. If you have more friends, you won't concentrate on this one person.
As for the body ... young, don't worry. Exercise properly, communicate more ... occasionally play games or something (but don't get addicted). Don't worry, let yourself be open-minded, and any illness will surround you.