How do i end this relationship?

Just tell her you think you should be alone right now. You guys are only 13 so you are still growing and changing in what you like and don't like. Tell her you can't be in a relationship right now. She will be hurt no matter what. Some girls tend to build relationships up in our minds, and from the sound of the monthly celebrations she's one of those girls. Better to end it as soon as possible rather than drag it out until its an even bigger mess.