He doesn't understand?<br />
Or you don't explain?
Tell him it's because of your depression but you still love him. If he still doesn't understand then how can you be with someone who doesn't care enough about you to try and learn a little about something you're going through...<br />
I was in your position about 2 years ago. Really bad depression. My partner was more understanding than I was because he took the time to listen to me. Now I'm a bit better but I still have bad days and he rarely questions why I'm in a bad mood, only if it's really bad.