My son has always been sad

Hi ladies! I'm a momma looking for help! I have an 18 year old son. He changed a lot about 4 years ago. He was always happy. Talked constantly. Enjoyed church camp. Loved to read and play video games. Then 4 years ago he changed. He no longer wanted to go to summer church camp. He talked a lot less. He didn't seem depressed per say. He wasn't lying in his room all day and refusing to eat. He just stopped talking. Mainly listened to music and only looked sad. I would ask if he was ok and he said yes. Even people at his school and our church noticed he changed. Last year he told me he was gay. So I figured that must have been what was wrong. He was struggling to come out and worried about our reaction. I figured since he knew we loved him he would be ok... But he still seems so sad. And whenever i ask him he puts on the fakest smile and says he's fine. I am so worried about him🥺