Why do I feel empty inside?

For a long time now (over 2 years) I have felt like nothing matters at all. I don’t care what happens in my life most of the time but I know I should. It’s like there’s a little bit of my brain that wants to act like a normal person but the rest of my brain holds me back and just doesn’t care. The only things that will get me to feel any emotion is if something really bad happens to someone close to me. Other than that I feel almost dangerous because I don’t feel empathy toward people I’m not close to. I could honestly kill someone and look them in the eyes with a straight face while I do it and it would be like nothing. I can’t really feel positive emotions either. I have a decent social life and see many of my closest friends everyday but I don’t get how they like me. All I do is sit there quietly with a blank stare the whole time. If we’re in the car I look out the window and just think in my head. If we’re anywhere at all really that’s all I can do. I want to do and say so much but I can’t because I’m very socially awkward on top of feeling empty. I just want help so I don’t have to live like this anymore it’s driving me absolutely crazy. I’m a young adult male if that is of any importance.