I need advice...

My fiance's​ exe keeps messaging him. These aren't the regular "hey", "I miss you", not even the "Wanna get back together?" messages. The messages she sends him are the size of mini novels, she is obsessed with him. She is pissing me off to the max, I have her number in my phone due to the fact he screenshoted her first few texts and didn't block out her number. I really don't know what to do. (Those are the two he blocked her number out on)