Hi, I know I'm not qualified to give advise but have you thought about seeking some sort of counselling?
You have taken a huge step in confiding with us all here how you feel, and someone who is trained would probably be better for you to talk to one on one. they can maybe help take that next step in the right direction of where you want to go in life.
I understand how you feel when you think what is the point in going on, I have felt like it myself plenty of times, I too seem to have been dealt blow after blow from my violent father who was a b***** to my mother and my brothers sister and I, I have lost four babies to of whom were twins and then my mother has been battling cancer for over 3 years now and is facing the prospect that it may have returned for a 3rd time.
Please though if you ever feel that it is getting all too much don't do anything to yourself, make a visit to your GP and explain to him what you have told us they are there to help.
plus you can always post a message on here as you have been doing there will always someone here to cheer you up.
Just think about how your family would miss you and how some of those people you have helped in your charity work are maybe in an even worse position in life.
I hope I have made sense and good luck with what ever you choose to do. I wish you all the best.