1) Dragons swear, humans swear, everyone swears once it their life. Prove me wrong.
2) Oasis was very strict about who could challenge her to the throne (3 at max, killed anybody else), so they were secretly a couple so they wouldn't get murdered. (Dragons also don't mate by sleeping with each other in a bed, I talked about this on a different image.)
3) Thorn and Smolder broke up because she didn't get the message from him that he was becoming a rock under a mountain, so she thought he just abandoned her, but it is hinted they meet up after the whole arc 1 fiasco.