How to help my crush with depression?

He rejected and pushed me away before due to his depression. I didn't realize he has depression at that time so I backed off. We haven't talked since then and his mood has been worse. Recently he has been very stressed due to work so I gave him a handmade encouragement card. However, I feel like he is more depressed after that as he keeps sighing and looks down most of the time. I don't know if my card is a backfire or not since he still has it in his desk everyday. Should I just leave him alone because I can't help but feel like I am one of the causes of his depression. I'm feeling so horrible!!!
How to help my crush with depression?
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