Do you have a proper advocate via the Carers network- MIND can help with this? sometimes we need another person to do our talking for us because we are all talked out.
Your making the effort to post here suggests to me that you can see the reasons for trying to get well. That you know deep down that nothing on earth will heal the scars left on your family should you commit suicide.
You may feel they are better off without you. Have you talked to those bereaved by suicide? I challenge you to find one person who will tell you
a) They are now better off without their loved one
b)that they would not wish that their loved one had tried again to seek help;
Have you ever been admitted for in patient treatment?
if you are truly considering suicide (have you thought of a method? Have you made any plans? Have you 'tidied up' your admin such as made a will etc?) then this tells me that you may need treatment that is hospital/clinic based.
Do you have a Care Co-ordinator/Case Manager/CPN? If yes, call them first thing tomorrow. tell them. show them your thread. If no, go to your doctor and be honest. Take a friend. But be honest about your suicidal ideation.
My gut instinct is that if there is help out there, you want to take it. You still have a little kernel of hope under that terrible depression. Hold onto that.
Use your support network.
Please give them another chance to help you.
It is not your 'place' to decide whether your loved ones will be better off without you.
I wish you luck.