Hi, Cutie and welcome,
Your question is a valid one, and something that most of us deal with day by day. I will speak for myself and let the others give you their input.
My depression which I have had for over 10+ years was due to a lot of things and yes, it most certainly effects your partner. If you are depressed, then your partner may thik it is caused by something they did. It will make them think that perhaps they are the cause of even that you might not want to be in the relationship at all. If that's the case, honesty is better then wondering and being depressed and causing their depression. At first onset, I let my depression run my life and my family as well. Being around a depressed person is no picnic. Others avoid us at any cost. I know mine did me. So, over the years and with the help of my "HP" wich is the Lord Himself, I have learned to control my depression between all the prayers and the right meds I am doing much better but I am in a stressful state also because I have Lupus and that effects me every day. I am fighting more than one battle.
Depression is a very real illness, one that a lot of people think it's in our head. They think it is bogus but it's not. Sometimes I can control my depression by thinking of good times and nice thoughts of my grandchildren or when my girls were younger but there is also a lot of pain too so that also comes into play. The first thing you have to do is find out what is depressing you and take it from there. See your doctor or even a counselor. Perhaps they can help you. The other members will also give you their imput too and they ae very wise. We are just a plain old fashion family here. No faces, just names!