I've been taken advantage of, too, so don't feel like it's just you.

Due to this unfortunate fact.....I find myself less enthusiastic to make friends and get close to anyone new.

Maybe we just need to be rude and mean upfront. Set the tone. Make people not want to ask us for anything! I'm just kidding.....but I wonder if that's what it takes?

I wouldn't dream of doing what some of the people you've described have done. I wonder what makes some folks feel justified to ask for so much?