You are NOT stupid, selfish, or weak!
It's not going to be all roses, but more like a rollercoaster ride, you'll have good days and bad days. Right now, you're having bad days, but you'll come out the other side, you just have to take each day as it comes, and just keep breathing.
Please don't keep this from your partner, you need his help and understanding. Wouldn't you want to know, if it was him who was ill, and was feeling so down? Of course he was happy that you were happy, but that doesn't mean he won't want to know when you're not.
It would also be a good idea to see your GP again, your dose might need to be increased for a while, until you get on an even keel.
Be kind to yourself, stop putting yourself down, you're none of those things. What you are, is a poorly person, who needs some extra love and caring at the moment. And you deserve it.
Sending you a great big, unmumsnetty (hug).