Great post, I know exactly how you feel. In fact this was me just a few years ago, but I got tired of always being the nice guy, the one everyone could count on.. It just got to be to much for me because like you said no one ever stopped to think and help me out. I think I got used it all up in this world of take take take. Now I am a recluse and it suits me much more. Sure it can be a bit lonely sometimes but it is a nice change of pace from the first 30+ years of my life. Keep on fighting the good fight as long as you can, but one day you will have to learn to be a bit more selfish if you truly want to enjoy life. ;)
Like you, I saw the light a few years ago. The phrase "you're my last hope" kept popping up and I began warning people that this would be the last time I would help them out without reciprocation. They would always promise but never deliver. So I started cutting people off.
They don't realize that warm-hearted people need help, regeneration and a rest once in awhile. I've seen too many get ground down trying to save the world, when they really need to nourish themselves...