husband depressed?

My husband is supposedly depressed. i think he does have some depression, but some of things that have happened make me believe that he is using this to keep control of our relationship.
do depressed individuals just treat their loved ones bad? everytime we talk on the phone or i am around he is sad and depressed. as soon as one of his friends comes over or he talks to them on the phone he is fine. very bubbly and talkative. he won't do anything with me. he goes out with his friends constantly planning things with them. if i ask to do something he already has plans.
it just seems odd to me that he can change his moods that quickly. when i think of depression, i think that it would be difficult to change so easily. you are unhappy for a period of time and then maybe later happy. not who you come in contact with.
i don't know. there is so much more to our story that i am sure it is hard for anyone to give advice.