Well this is some sad news to report.
Both reps for the actors couldn't be contacted, but sources tell Jared that:
Their three years together just ran its course. They have so many great memories together but couldn’t make it work in the end. The break-up was amicable – there was no drama whatsoever. Emma and Evan are even still friends!
The couple have been together for three years, having met when they both starred in the film Adult World back in 2012. They got engaged the following year. They also starred in two seasons of American Horror Story together.
Evan is currently filming the next saga in the X Men franchise; X-Men Apocalypse while Emma is next to star in the TV show Scream Queens due out in September 2015.