How can I learn to stop caring about other people's opinions?

When i was between 12 - 13 years old I honestly barely cared what others thought of my opinion. If you did not like me, I did not like you. Now that I'm 19/20 years I seem to have evolved into a people-pleasers. I always feel like i need friends and support. I never used to be so desperare. I am settling for guys I am not really attracted to that steal from me, lie to me, and find ways to make me feel inferior. What is wrong with me?