Queen, I am sorry things are so rough.
I may have some inkling what you are going through. Like I said, i was depressed for a very long time myself. I have been on a psych ward. I've tried to kill myself. Things were really, really bad for a very long time and I thought they would never get better. I was lucky that I was finally forced to see a psychiatrist who turned out to be fantastic and saved my life really.
It's not that I can sit here and say the depression will never try to come back, the difference is that now I have the tools to keep it from getting really bad again -- things I can do on my own, and knowing what resources I can turn to if I can't handle things on my own. If you were to manage being depression-free for five years, you would undoubtedly gather a set of tools yourself that would give you some confidence and hope that things could continue on a good path.
I know what you mean about not wanting to repeat your own childhood experience -- one of my saddest memories, when I was pregnant, was someone asking me what I would like to do that my own mother did, and I realised I couldn't think of anything 
When I was depressed, that was a big reason why I thought kids were a bad idea. Now, I am just sort of proud of myself for overcoming that, and determined not to repeat it, and hopeful that I won't.
One last point: I think that when you're depressed, you end up not wanting to address the depression head on and instead you come up with all kinds of work-around solutions to cope with big life decisions, like work and family etc. I'm not saying your desire for sterilisation isn't genuine, but it also strikes me that you have a lot of very complex and difficult emotions around childhood, family, relationships, etc., and that sterilisation might seem like a straightforward answer to eliminate all these issues without having to actually deal with them.
It's easy for me to sit here and say you should deal with your depression, I can only imagine what you have been through, but at the very least i think you shouldn't do anything that a future version of you might desperately regret.