Arrow I'm so sorry you've been let down and used by someone you helped and thought your friend. Because you are a true friend, you expect others to be the same to you and it really hurts as well as making you angry when someone acts so uncaring.
Just don't bother with that person in your life anymore, just avoid socialising or being around them if you can, or be polite but gradually more and more disinterested if you have to be in their company or work with them.
The best thing to do is to write it off to experience, but it is bound to make you less ready help and befriend someone new. BUT don't let it stop you making new friends, there are heaps of great people out there despite one bad apple - just be more cautious before you commit.
Wooooah - here I go sounding like what we call an "Agony Aunt" again