Wow. I'm super surprised that Raven didn't mention before now that Finn was responsible for her not being floated.
Which, totally makes sense as to why she's so adamant that he not be handed over to the Grounders. I mean, I thought it was 'just love', but it seems like she's literally indebted to him.
Eventually, Finn ends up giving himself up. Against, the wishes of our main cast. (The people who don't know him, or only know him as 'the spacewalker' are all for trading him to the Grounders for freedom.
Clarke goes to bargain for him, but the Commander will accept his death and nothing more. So Clarke kills him herself. I think we were supposed to believe she did it to alleviate his suffering (they were planning to torture him). But I think she actually faked his death and next episode we're going to find out he's fine.
I really feel like that 'Thank you, Princess,' was him acknowledging she was gonna save him.