I think its bc tennese feels guilty and thinks he doesnt deserve happiness bc he was a killer and when he is with amber he is happy, at least thats what I got :/
Adding to what ^ said, his past is haunting him, he’s with amber so that is triggering this trauma, because in his mind he doesn’t deserve it, so the more happy he is in the present the more his subconscious guilt accumulates making the current nightmare worse, with the hand ripping his skin. Amber understands that it has to do with him, so he feels responsible and ends up cutting himself to relieve his guilt, and now they are currently communicating that
I think the conversation is too complex to my stupid brain. Can anyone briefly explain what stopping them to be beside each other and happy?