I'm not exactly reading this story, but overall, I can see this story having multiple types of endings. I see this story as a way of having both abused and abuser develop and grow in the story. Finn, the abused, will start to develop more confidence in himself that he will never allow someone to demean and mock him again. Alfine, the abuser, will learn that she's been too harsh with Finn and realize that she needs to change to become a better person that should respect her partner more.
The endings can have Finn and Alfine get back together, both having grown so that Finn will no longer let her degrade him, and she will have learned to respect him more, and the two will treat each other as equals and have a stronger relationship as a result.
Or, it can end with Finn deciding that they shouldn't be back together, and Alfine agreeing, realizing that they might not be best for the relationship, but they will at least care about one another because they had been friends since kids. Finn already has a possible new love interest, and Alfine could likely find a new lover herself in the story.