Being alone is a funny thing. Sometimes it's good, renewing, and delightful. Other times it's alienating, foreboding, and unwanted. As parents, we want to understand and allow for all of the moods that our children may experience. He's been in his room by himself a long time now. Does he just want to be alone? Is he lonely? Is something going on? Rather than guess or hope he is okay, check it out. Seek him out and assess his mood in conversation. If he shows signs of an emotional fever, use your active listening to help him calm down. Encourage his participation in family time. Respect his privacy, while also reminding him that he is a part of family. His mood could be a symptom of other issues, such as anxiety, depression, or stress. Use joint problem-solving to help him find tools to address his concerns/issues. This is great parenting that generates teachable moments.