So quit this life. I can't argue with the misery you feel in this life, and niether can anyone on this board. If THIS life is miserable, then walk away from it.
Walk to a NEW one. Dedicate your life to others. Join the Peace Corps. Join a church-affiliated group that goes and digs sewer trenches in Ecuador.
Walk out on this life, leaving all the possessions, all of the trappings, and all of the baggage, behind.
If you can expend any amount of effort, labor, or energy, and make the life of another human being BETTER, then you HAVE a purpose. Digging a sewer trench, helping build a school, anything like that, IS a new life. Not only will the people not leave you, they will love you. And you will be able to truly feel God's love as well. You may feel like nobody to folks around you now. But once you give your life to serving others, you will be somebody -- somebody dear, and important -- the the people you serve. Become and instrument of good -- how's that for a purpose?
I am no clinician. But I have seen suicide up close, among family and friends. I have looked into the window of the darkest part of the soul. And I have seen a choice that could be made -- that could ALWAYS be made.
Leave all of THIS world behind. And go to a new one -- a new one where you are somebody, to someone. It is NOT wrong to want to end this "life" -- but it would be wrong to kill yourself so that after ending your current "life," you couldn't start a new one.