What is the word to call a buddy who only helps you, but never asks for help?
Solution 1:
You may use altruist.
unselfish regard for or devotion to the welfare of others.
Cambridge Online Dictionary defines altruism as follows:
willingness to do things which bring advantages to other people, even if it results in disadvantage for yourself.
Wikipedia has a page for altruism as well.
Solution 2:
Perhaps you could call that person a "guardian angel", meaning:
a person who looks after or is concerned with the welfare of another.