How can you help someone with depression?

Did your boyfriend/husband ever had a depression phrase? How did you deal with it, how did you make it better?

I think my boyfriend is bipolar, somehow, and in my oppinion, in some sort of depression begining part.. he is very irritable all the time, he is not happy about his life, even tho he has a good life, he’s not in the mood of doing anything, sleepy all the time.. also, he tells me things that makes me feel like he doesn’t need me anymore, but next day he is totally the opposide.. we had some problems, of course, but problems that we can get over it, for real..

I really believe something is going on, and its serious, not only some regular mood swings. He told me that he doesnt know why he feels like this sometimes, and that he thinks there is a problem out there, but he doesnt know how to solve it.

How can i help him? How should i act around him? I feel like i dont know how to be anymore..