How to explain how I’m feeling?

Been feeling really depressed/sad for a few days.

Visited my bf yesterday but he could tell I was off and now he thinks something is wrong in our relationship

:(

I honestly don’t know how to explain why I’m feeling like this so I told him I was fine.

AND THAT is adding to my crappy mood.

What should I do?

Should I tell him I lied about feeling fine?

Should I say that I’m going through a rough patch with myself?

He makes me forget my worries while I’m with him but I can’t always hide it.