What is my film about?

Changes of my film idea:

I have decided to make a short film focusing on the life of a couple - 1 male charactor and 1 female character. The film will focus on their relationship, showing the couple living together and being happy. The girls is approximately between 17-18, while the male is a little older around 21-22. The film will then introduce a female character who befriends the girlfriend and comes over for lunch with her at their home. The neighbour begins to manipulate the girlfriend over her boyfriend. Their relationship begins to fall a part. At the end the girl is seen running with blood down her. I have decided to make my film this way, as it gives me a chance to focus on the emotions of the character, the aim of a conventional psychiological thriller does. The film will show how the relationship changes, alongside the attitudes of the characters, leading to the murder!