Why did i forgive her?

my gf cheated on me wif my cozin. and after sometime she told me and we didnt break up. i went balistic and walked out. she kept calling and texting. but i never responded. now all i can think about is her. i dream of her i think of her. so i went to her house the other day, i didnt even get to her doorstep befor she jumped on me while she kept saying i love you. why did i forgive her?