I can relate to a lot of what you are saying. I dont hate anyone in this world like I hate myself - its a special sort of loating i reserve for only me. Im better than I used to be with it, but its still there and i can understand the feelings of 'why does my partner stay with me?' I get them every day. Shes wonderful and Im...well, you get the picture.
All I can say is that looking back can be decieving. I find a lot of my fond memories come from tough times and i have picked out the shiny bits to remember. This has the effect of making life look like it was better then, when in fact it wasnt - I just saw the world differently and coped better.
You are not worthless, please dont think that. Everyone at some point in their lives has touched the life of others and made a difference to their world in some way. How can an act like that come from somebody who is worthless? Also your partner clearly loves you and sees a wonderful person in you, so he is clearly seeing something that you are missing. To him you are not useless, and his opinion must matter to you? Does anybody elses opinion matter as much?
Take care x