Help please I don’t know what to do

My friend, I don’t know. It’s complicated. I like him. He like me. But that’s another story. But we we were just sitting and he said “I’m sad" and I was like “what’s wrong did something happen at school? Did I do something?” And he said no. Should I be worried? I asked him what wrong and he didn’t answer. What should I do? I’m really worried