Castiel stood alone in the playground after seeking help from Naomi, she said the only way he could get his grace back was to find his true love and when your bodies become one only then shall your grace return and only she will be able to see his true form and here his real voice.
"How could i find love?" Cas thought to himself. He barely understood it, let alone to try and find it was another thing, he didn't know where to start.
Besides Sam and Dean, the only person he ever had any kind of humanly feelings for was Eleanor, a hunter who had worked with him and the Winchesters.
She was with them for about 3 years before she left on her own 2 years ago. Even then Cas never understood why he felt strong feelings of loss after she had kissed him on the day she left.
For weeks he didn't know why he was angry and snappy all the time, moping about the bunker.
Sam and Dean had to tip toe around him, afraid he might smite them back to hell, until when he was held up in his room binge watching episodes of Grey's Anatomy .
Dean even tried again to get him laid but Cas wasn't interested in putting his hands on any other woman.
When the boys finally got Cas out on a hunt he had gone straight up Blade and slaughtered an entire vampire nest of 11 all by himself.
"Damn it Cas, you got some kind of death wish?" Dean said to him. He was really upset at him for being so wreckless, but Cas didn't care, he was centuries old and very skilled in battle and what better vent his anger out on.
Castiel snapped out of his thoughts and left the playground. He didn't expect to get help from heaven but it was his last hope and now, he had none left.
Cas arrived back at the bunker thinking there was nothing left to do but leave. Sam, Dean and Mary were out working a case with Bobby thankful they weren't around to stop him from leaving.
He went strait to his room and grabbed a duffel bag out of the closet and packed up the little things his human self would need. The little clothes he had, underwear, toothpaste, a toothbrush and soap, along with a shaving kit Dean had bought for him when he lost his grace, a 9mil with a few rounds and his Angel blade.
He still had his fake id's, a credit card Charlie had given him and a few bucks to help him get by for a while until he found a job.
Cas left a note on the Map Table not saying when he would be back and that he borrowed the pickup truck. One that they never really used. He swung his duffel over his shoulder and took one last look around the bunker, then left.