Absence makes the heart grow fonder only if deep in your heart you treasured whatever has become absent. When something is there, you tend to take advantage of it. When it's gone, it's only then that you know how much you actually treasured it. That's why when two people were in love and one suggests a break, the best advice is for the other to just back off and give the former some space. He or she can then choose whether he or she wants to continue this relationship and blah blah blah. If absence does make the heart grow fonder, he or she would come running back.

About the second question, I am not very sure. I wouldn't put a definite answer on that one.