teenage boys and love

sometimes i really don't understand how guys work. What is up with all of their, i love yous to so many people when they don't mean it. What is their end goal with all of it, what are they gaining other than an ego boost. Last year around this time, i thought he loved me, but now i know he didn't. He got what he wanted and than he left. Now he's doing the same thing to another poor girl. What happened to him that make him absolutely numb to other peoples feeling

Feeling: sorry for her