Why does Edward try to kill himself?

Edward trys to kill himself because Bella goes cliff diving at La Push. Then Alice sees her in one of her visions and thinks she is trying to commit suicide. After that Alice tells Rosalie (her sister). However, Rosalie can not keep a secret so she goes and tells Edward. Since Edward is so madly in love with Bella that he trys to kill himself because he thinks with Bella dead he feels he has no reason to live.

Alice goes to check on Bella to make sure she didn't actually commit suicide. Then her and Bella rush to try and find Edward before he exposes himself to the humans. Luckily, Bella reaches Edward before he can show the humans he is a vampire. If he exposed himself to the humans the Volturi would kill him becasue he almost revealed the secret of being a vampire.