How do you set boundaries after a good deed goes unappreciated or is taken advantage of?

Is there any emotional support groups for children financially supporting parents? My father died 31 years ago. The money is one thing, but being the man having to make all the decisions is not helping my depression.
Why do people lose their social inhibitions so quickly when they are on stimulants?
Who usually dictates the social terms of your arrangements?
Why do some people reveal their true colors only after they feel comfortable in a relationship, like not paying for their share?