Dear Armadillo - I hope you read this in the morning when you wake up - you say your mum loves you but it sounds like she has systematically taken you apart from quite a young age and made sure that you have no idea of your self-worth - this is not a loving action.
I'm sure she loves you in some way but the way she has treated you is not loving at all, far from it. Parents should encourage their children to be independent, not destroy their abilities to be so.
I wonder whether your ma had her own problems with depression etc when she was younger and saw that you were following in her pattern; or whether some other member of her family had depression and she had to cope with it. It is amazing that she refused to allow you to be treated and I would guess that, if she has always been this down on you and negative towards you that she may well have contributed to your depressed state!
You are a worthwhile human - you have a DP, a lovely DS, a job (so what if it's not hugely exciting/well-paid - at least you're not taking handouts without giving something back!).
My own mum, God love her, used to put me down a lot in my teens - but it turned out that she was jealous of my opportunities that she never had and that her own self-confidence was terribly low (you don't realise this when you're a teen, only later). I ended up with depressingly low self-confidence and almost became a depressive too. I don't know what saved me but I used to have days at a time in a black hole where no one could reach me.
your mum is definitely an emotional/energy vampire (or leech if you prefer) - try to imagine that you really are an armadillo with armour-plating when you have to see her or talk to her, and that her poison arrows cannot pierce your armoour so she cannot suck your energy away.
I hope this is of some help to you - and don't let anyone tell you how lucky you are to have someone like her controlling your life - they don't know the full story.
hugs to you