Or he wants you to see his sadness in this way. See if you can contact him and care about him, maybe it's someone in your circle of friends, maybe he's only visible to you.
I just want to send a circle of friends to make myself feel better. This is also a way for him to heal his lovelorn love, without thinking too much.
Let bygones be bygones, don't care too much, he will forget after a long time, as long as you don't contact him. This is also the best way for him.