Sometimes in relationships, it's more than just stating the diagnosis. It's about expression of your relationship needs and how it affects you. For instance, I sometimes get anxiety attacks. I may need to sit down and have a glass of water.
I do have a depression diagnosis on top of anxiety. Being able to convey my triggers can be helpful. I might only need to have my hand held or just lay down for a bit or may need to get out of the house and distract my mind. Understanding your needs is important in letting your partner know about depression. Your therapist may have some individualized suggestions based upon personal knowledge.