Hi OP.
I don't know what it's like to suffer physical pain for years that it causes depression. I couldn't begin to imagine what that's like, but I know how hard depression is to live with. I understand what it's like to have that monster within. To have all the joy of things you used to love sucked away. To feel upset from the moment of waking to the time you sleep, that is if you get much sleep at all. I know what's it like to want to end it all.
I felt the same once. I almost went through with it. I was going to OD myself. Painless way to go. Just like falling asleep, but the difference this time would be I wouldn't wake up and all the pain would be over. I would be in peace and my loved ones wouldn't have to put up with me again.
Thinking about my loved ones is what stopped me. The thought of my wife and child finding my body. That would cause them a world of pain and suffering. I would mentality scare them for life. It was then that I knew I needed help, and not just support from my family, because a lot of people still don't understand depression. I'm not trying to guilt trip you here, but you need to consider the impact your actions will have on other people.
My advice is to talk to people and seek professional help. If you're like me than that's easier said than done. Talking to my wife and family about it was hard enough. The thought of talking to an absolute stranger about the way I felt seemed so alien. It was tough, but taking that first step and seeking real help was the best thing I ever did. I'm not sure if you're ever cured, but I feel a completely different person to the man who locked himself up in the bathroom, complete with a full packet of paracetamol.
Many people think you can just "man up" and will yourself out of depression, but it doesn't work like that. The only way to get better is to get real professional help.
I know you want to end your life, but it's not the answer. I don't know who you are, where you live or really anything about your life, but I know there are people on this planet that love you and need you. You still have a life and a choice on what you do with it. Don't let depression win.
All the best OP. I really hope everything works out for you like it did for me and the millions of others who beat it.