Most Helpful Guy
You have made a mistake my firend."Maybe" doesn't mean "no", maybe means maybe. It is natural that he saw that act in a bad way. You could just say "no, sorry" next time, you wouldn't be rude, you wouldn't get misunderstood either.
Combining his depression with this misunderstanding might have caused him to end the relationship. Also long-term relationships put emotional burden on people. He could have thought he couldnt endure that or couldnt make you happy. People could lose their trust for people they love, in depression.
What can you do now? Give him a little time to stay alone, or with his friends. Do not approach him for a while. don't give him a deep, bitter gaze when you make eye contact because he left you.(some girls do this, dont take it personal) If he feels better, he might start talking you again or you might approach him if you feel it is the right time. When that happens talk about his personal problems and your relationship in a sincere way.
And keep that in mind, i dont know you or him. If you have a common friend who is wise and objective, talking to him\her maybe helpful.
Most Helpful Girl
He's wasting your time