I want you to remember that this is just my opinion on what I think might be happening. I am a little puzzled because in reading your post, a couple times you say that you do not have a good relationship and then you say you do. The impression I get from that is that your happiness depends on how he is feeling or doing. Although I know that it is hard you must decide if this relationship is healthy for you. Are you always walking on egg shells? If your answer is yes, I would seriously consider the relationship and what you get out of it.
That is the hardest thing to do but if you want to get better, depression included, you must "soul-search" and really listen to what you are saying. Intuition is usually right on.
As far as him being distant, it sounds to me as if he was trying to do that when you guys were together by working or fighting. There could be a lot of reasons he is pulling from you. Could be the depression or other circumstances that you cant control.
If he will sit with you have a heart to heart with him and tell him to tell you the truth no matter what.
I wish you luck.