Tripleplay,
I know it's hard to not become jaded, not become numb. You are going through some very tough times, but you are going THROUGH them, not staying there.
There was a time that I believed in being a good guy and helping people with all of my might, all of my energy. Then I was abandoned and worse by many of my closest people in life all at the same time and for no reason, by the people who pretended to be good hearted people then turned around and stabbed my back and tried to ruin my life. Like you said, life felt meaningless after that. So I drifted, never did anything bad but I just gave up trying to help or trying to love.
But eventually I just changed my mind. I'm not going to let anybody change who I am. I know that people will sometimes or maybe often treat me like s**t. But I'm going to fight through that. If the world sucks then its up to me to make it better. If the world is full of disloyal, mean-spirited people, I'm going to do my best to be loyal, to have a good heart anyway.
What you do DOES have meaning, DOES make a difference. Picture yourself fighting through a hurricane.