Dally is not able to see any other way to deal with the frustration and then grief which pervades his life. The only person who Dally really cared for was Johnny - more thah he even cared for himself. He saw that his hard exterior was a weakness, but then Johnny's nobel character proved to be a weakness too. Dallas sees all life as futile after Johnny's death.
Of course Dally wants to die. Dying is so much easier than living and overcoming the obstacles in the way of what he wants to achieve. Had he not wanted to die, he would not have raised the gun towards the cops. This is a real phenomenan known as suicide by cop.
I think that Dally's suicide was caused by the death of Johnny and the immense loss that Dally felt. He knew that both he and Johnny had been failed by the system and that for him, like Johnny, death really was the only escape. I think the drama of dying at the hands of the police, rather than alone, appealed to his need for recognition as being a force to be reckoned with. He had no control of Johnny's death so needed to have control of his own.
! i think he just died because johny was so close to him and he loved him so much, he couldn't live without him, so he...... choosed to died. that might be one reson.
In the book The Outsiders, Dally has spent his whole life engaging in self destructive behaviors. He was a juvenile offender before he had moved to the place where he had met Johnny and the rest of the Greasers.
Dally is also a person who has inner rage that he releases on others including picking on children. Yet, Dally found in Johnny a relatively innocent person who was in need of protection. For Dally, Johnny was the opposite end of who he himself was and so he loved him and allowed himself to be loved.
When Johnny dies, Dally just freaks out and responds in the only way that he knows how to cope. I don't think he was trying to commit suicide so much as he was responding in an impulsive manner and self-destructing without really thinking abut it. Because he had called for Darry, I believe he was reaching out for someone to help him to stop from further spinning out of control.