How Does Bonding With A Dog Happen?

My Female Pitbull-Boxer had nine puppies; I gave away six of them and kept three---a sweet female black Lab and two male Mastiffs; I thought I was going to bond with the one male (Kilo), but it happened with the other one (Chico) instead! It's cool because I love Chico VERY much!!! It turns out that he is also the LEADER of the pack! I would like to know how the BONDING between us happened! Any ideas??? Gracias!