Have you been diagnosed by a medical doctor or mental health professional with depression?

It sounds like you have told your boyfriend that you think you may have depression.

If you get an official diagnosis of depression and/or anxiety, I would certainly tell him. And if you are feeling very sad and feel like you're not being yourself with him, I would tell him that you feel really sad and not like yourself.

Other people may give you different advice, but I have found that most people who haven't experienced depression don't understand when you try to explain to them how it feels inside your head and your emotions. If they are the type of person who wants to know what it feels like inside other people's heads (a minority of people in my experience) they may listen and then say "Oh wow, I don't know what that feels like.")

Lots of people will start trying to "fix" you or make suggestions to you to help you feel better. They may even be good suggestions, but depending on your frame of mind, you may or may not be able to use that advice.

I think you have to decide what level of detail is appropriate to disclose to other people (even your boyfriend.)

It's perfectly okay and good to tell your boyfriend what he can do to help you when you're feeling sad. He just may not be able to understand or use all the details about your feelings.

If you haven't been officially diagnosed with depression, I would encourage you first of all to see your primary care doctor and tell him/her about your emotions, mood, and physical symptoms. They will need to decide if they need to check you for anemia or thyroid disease or vitamin deficiencies or other medical conditions that can cause depression.

You mentioned your mom in another post, so I'm assuming that you are in high school or college and may need to tell your parent(s) first before you see a doctor. If that's not correct, sorry.

I hope that you'll let us know how things go with you. These forums are a good place to express your feelings and to get advice and support.