I guess I get why everyone in the comment section is unsatisfied with how everything ended. When you build a story around sex instead of adding sex in a story, it's not going to be that good or make much sense for that matter. They call themselves loving each other but it was really honestly only lust but still kinda cute nonetheless.
It's okay the ending is kinda wired. Maybe one more chapter would be good. The think with the sister was actually a sick plot move that could be huuuge and the think with the tear and the narrator also nice. The sudden sex was just not good.