What's the Name of That Book??? discussion

I read this in 2015-2016 and I can't seem to remember the name. It's a book about how this girl was dating a guy, he gets into an accident in a hit and run. She goes to tag him in a facebook post (i think) and someone else comes up (like automated tagging) she looks through this other guys profile and they look the exact same. I think she goes to a party he goes to and throughout the novel she like finds clues and realises she doesnt know him as well as she thought. And at the end there is a big reveal that it was the uncle and then he kills himself by jumping off of a waterfall I think??? I also think the cover had like a blurry blue background with a carosouel or like a polaroid? please help.

Lily, is this book for adults or teens?

I removed the ALL CAPS from the header (it looks like shouting) and added a spoiler alert.

Forget Me by K.A. Harrington?

Yes!!!! Thankyou Becca