If he cares about you he'll be understanding... No one should expect their date to be a 24/7 source of joy and cheerfulness. Mind you, I think any reasonable guy would appreciate being "your rock", someone you can lean on and trust with your darkest feelings, etc. In my opinion, just having the opportunity of going out to eat something with you would be a privilege, and I think the onus is on him to steer the conversation towards things a little more specific than "tell me about yourself". If you feel the date went terribly wrong you may text something along the lines of "sorry, I was not in a good mood today", etc. If he's a worthwhile person he should see all what you are, past your depression...
