How do I explain my depression to my partner?

He knows I'm bipolar and what it entails but I don't think he fully understands. I've been feeling blue lately so my libido is low and I feel the need to isolate myself. We keep getting in arguments because he thinks I'm just being cold and distant. I haven't really been helpful around the house and he thinks it because I'm being lazy. It's really hard for me to communicate how I feel because it's painful. I really don't like talking about my depression even though I trust him.

I know it's easier to say what needs to be done.

You love him then you should tell him. It will help both of you.

He will think you're acting negatively when you actually need him the most.