Why do Edward and Bella want to get married?

He loves her and she loves him! Even though he is a vampire he doesn't want to be a monster, yet he doesn't want to have died back in 1918 from spanish influenza.He wants to be with Bella forever. And to make sure that she is his and nobody elses. Not Jacob's or Mikes' or Tyler's or Eric's. He wants to be with her forever, and never lose her.

However Bella is reluctant at first, as she is unsure about marriage after the divorce of her parents Charlie and Renee.

However she wants to try new things in her realationship with Edward, which he will not give her until they are married. They become engaged in Eclipse, and marry in Breaking Dawn, where she finds out that her worries about marriage and marrying Edward have dissapeared on the actual wedding day.