1. Girls also come back, although they do it subtly.
  2. Men do not always mess it up. It is due to differences in processing of information in both male and female brain.
  3. Men are short tempered but kind hearted.They have the guts and ability to accept their mistakes while most of the ‘feminine ego’ does not take rejection well.
  4. Men connect deeply wiht some girls.On the surface they look like care free and ‘not giving a fuck’ type, but deep down they really care of their girls.Men are possessive as well as protective.Some times they return to protect you as they know your nature as well as nature of other men!
  5. Men do not always want sex from you.They want companionship at times.
  6. They do find ways to contact you because they know that your attention seeking and ‘bestowed with surplus attention’ feminine ego will never do that.For some girls it might be shyness but doesn’t seem true for now a days ‘progressive’ girls.
  7. Our mind has positivity bias .Over long period of time we tend to forget negative details. Since men have short memory (opposed to women), they easily forget your faults and remember only positives.

Source: Is it true that men always come back? – Quora