To begin with, Castiel doesn't know how to feel when Dean meets Cassie. He expects Dean to move on at some point, obviously, but even though it's been three whole years since they spoke (something that makes Castiel's shoulders heavier every day) he still aches for the thought, the possibility that there's space in Dean's heart for him.

They meet on a hunt, as usual with Dean's dates and girlfriends, and of course thing advance quickly. They're important to each other, it's obvious, and Dean is happy, so Castiel decides it's a good thing he's with Cassie.

Dean still hunts, and it's obvious that it annoys Cassie. She probably thinks he's cheating on her, Cas thinks. It's not you he's cheating on, his brain adds, and as much as he knows it isn't true, it's how he feels.

There's a blowout over it. Castiel sees it all. Dean comes back from a hunt with his dad, and Cassie's waiting for him, hands pressed against her hips and her mouth a flat line. Dean stops like a deer caught in headlights, and even Cas can't deny how guilty he looks.

'Where were you?' Cassie asks.

Dean's face is torn; Cas knows the truth, but that's because Cas is part of Dean's life like that. But Dean never tells anyone about that part of him. He has to choose what to do.

Dean goes with the truth. He spills everything, being a hunter, the creatures he hunts with his dad, even Sam leaving. Cassie's disbelief becomes more prominent in her face the more Dean explains. Cas can understand why she wouldn't believe him, humans do have a hard time believing that monsters are real, that they are really in danger, but surely she knows Dean loves her and wouldn't lie to her.

He offers to show her inside his duffel, where he has some stakes and holy oil and other weapons, but she doesn't believe him, doesn't want to see.

Dean's face breaks as he realises she doesn't believe him, asks if there's anything he can do to make her believe him.

She insists there isn't. 'Dean, if you want to break up with me, just do it. There's no point trying to protect my feelings or whatever it is you're doing if you're not happy.'

'But I am happy, I swear, I'm not lying to you.'

'You realise you sound crazy, right?'

'I know, but why would I lie to you?'

'I don't know Dean, but that's more feasible than some kids story about monster hunting.'

Dean looks hurt, as though her words delivered a worse blow than his father's fists ever did. 'Cassie…'

'I can't,' she says, hands dropping from her hips, falling to her sides, palms facing him.

He takes a step closer, but she stops him. 'Don't.'

'Okay.'

'Dean, I can't do this. If you're going to insist it's because it's the reality of it, fine. But I can't do it.'

The Winchester is shocked. 'You're breaking up with me?'

Cassie nods, tears in her eyes. 'Goodbye, Dean.'

Dean's shoulders are low as he walks to his Impala, bearing the burden of his loss. Cas wishes he could do something to help.