The Swans and the Cullens have always been close. Charlie and Renee Swan were best friends with Esme and Carlisle Cullen since college. Carlisle Cullen was the leader of the largest mafia in the world while Charlie Swan was the chief of police. Renee was a school teacher while Esme was a stay at home mom. Esme and Carlisle had three kids, their daughter Alice and their sons Emmett and Edward. Renee and Charlie had a daughter Isabella but she preferred to go by Bella.
Either the Cullens were at the Swan's house or the Swans were at the Cullen's house all the time. The holidays were spent the same way. And all the kids were best friends with each other, even though since the age of eight Edward declared to everyone that one day he was going to marry Bella. Both sets of parents always wanted that to happen and couldn't image Bella or Edward with anybody else.
It was the one wish that both sets of parents shared to have Edward and Bella to get married and to be together. In the minds of Esme, Carlisle nobody was good enough for their son but Bella and in the minds of Renee and Charlie nobody was good enough for their daughter except for Edward.
Edward has always been over protective and possessive of young Bella and as time went on and the two grew so did Edward's possessive and over protective ways regarding Bella. One day when Bella was four a kid named Connor who was attending Bella's birthday party decided to steal Bella's ice cream cone and that did not sit well with eight year old Edward who marched up to the Connor grabbed the ice cream cone out his hand and handed it back to Bella before he gave Connor a black eye for messing with his girl and making his girl cry. Edward then proceeded to walk over to Bella and wipe her tears away with this fingers and then kissed her cheek. All the adults thought it was so adorable except for Connor's parents who scolded Esme and Carlisle about Edward's behavior before Esme told them where they could stick their parenting advice and comments about her son. After that everyone referred to Edward as Bella's protector.
At the age of six, the Swans' house was broken into and Charlie and Renee were shot and killed in their own home right in front of their own daughter. Bella went to live with the Cullens because her parents will it stated that if anything happened to them that Bella was to live with Esme and Carlisle Cullen. When Bella was twelve Edward kissed her for the first time. For Edward it was a dream come true since he was already in love with Bella. So then it only made since for Bella and Edward to start dating even though Bella was twelve and Edward was sixteen.