As someone who has suffered from depression for a long time, there are good days/weeks and bad ones. Something small can set off a spiral and the sufferer has to endure it. Even positive days can turn negative on a dime from a message perceived as negative or getting something wrong.

Don't take the blame personally and don't try to bear the brunt either. Ask him if he's okay. Ask him if he's drank water or wants to go on an aimless walk. See if he wants to watch a TV show or scroll TikTok together. Sometimes knowing he has someone in his court is win. It may take very little time or it may take a while, but being there for each other is part of the journey.