I know how you feel - I had a similar issue with my partner, who thankfully has been very understanding.

Are you able to talk to him about what is going on? Explain your depression and what it means? If you don't feel comfortable talking, could you write to him? Tell him that you really do love him but sometimes the depression takes over and it is hard to show your emotions and love. Tell him in advance what happens when you become depressed (what you feel, what you think and what you want/need from him) so that he can prepare and also not be shocked when it does happen.

Unfortunately it is quite common so there are probably also online resources you could encourage him to look up if he is wanting more information.

Any kind of mental illness can be hard on a relationship but with the right people it can still work. It involves trying to be as open as possible and communicating what you are feeling when you can and also explaining the kinds of things that you may be thinking or experiencing later on when you do withdraw so that he knows what might be happening and what you want him to do.

Good luck

Oh, and welcome to PsychCentral.