Unrequited lovee

(TW:blood,su!c!de,Murd3r,psych0path!c behavior etc.)
This book is about a girl who doesn't know she has hanahaki disease as she feels come to complete when she's with her best friend and as to prevent the person she loves from falling in love with another she uses various ways to end or ruin her rivals lives all to gain his love and confess to him under the cherry tree in the park before it's too late.