In life you will realize that there is a purpose for everyone you meet. Some will test you, some will use you, and some will teach you. But most important are the ones that bring out the best in you. Those are the ones worth keeping around. :) So true.
Meredith speaks the truth in this scene. It is the most terrible thing thinking you have a chance with someone then you find out they belong to someone else so you have to let them go & sit back & watch them love that other person