Im sad, because ive fallen out of love with my girlfriend, but dont know what to do anymore?

We've been ating for over 2yrs, and shared so many happy memories, but my Sister who was my personal hero just passed away a few weeks ago, and ever since that ive foundmyself not loving my girlfriend anymore, and worst part is that she gets mad easly. IDK what to do, I dont want to hurt her with a break up, but this relationship isnt getting any better..... Pease give me some helpful advice :((((