Should someone be obliged to support an adult sibling who has made wrong relationship choices more than twice in his/her life?

I am totally all for siblings supporting each other and I truly believe we should go to the ends of the earth to help a sibling in trouble. After all that is what family is all about. Family always first! That being said, is it not going too far when an adult sibling who can’t get his/her life together and keeps making silly relationship errors that lead to his/her demise, expects her/his brother/sister to come to the rescue? I am not talking about health issues where help should be granted, I mean the person not being able to stand on his/her feet and expecting brother/sister to come and fish him out of trouble.
Personally, I think it is irresponsible and exploiting behavior. Correct me if I am wrong please!