Eren is a little sceptical about the weapon thing. This is about trust or some shit? Please. He's the least trustworthy person he knows.

But…does Reiner know that? Actually, now he's not sure. Reiner has no idea about all the lies and half-truths Eren has told, even in Ellipsa. It's hard to stop being a liar, he's found, even if he largely does it to spare other people from his horrors.

All of that aside, though, isn't what they have based somewhat on trust? It didn't start there, but somewhere along the line, it became that. It took trust to let Reiner fuck his face like that one time, and that was before he'd decided to trust. It took trust to tell Reiner some of his shit there in the dark.

What do you want to be?
Alive.

He'd never said such a thing to anyone else, only to Reiner.

They hadn't killed each other as titans and they could have.

When did he forget what it was like to trust someone? Obviously Reiner has broken his trust in the past, and he has broken/will break Reiner's in return. For now, though, this is still stolen time.

Reiner asks him a question and he shrugs.

"I don't know. I only know how to use guns and swords. What about you?"