Would I BE Wrong To Leave????

Recently my finacee' purchased a dog for her daughter's b-day. The problem is I am allergic to dog hair and dandruff & I despise going to the doctor for anything. Her b-day was 7/25/08...on 7/21/08 she walks into my office (I work from home), and says "I've made the decision to get her a dog!!!)". Now she wanted one last year for her b-day (we've been together for three years) but her Mom said no because of my allergies. What gets me is I want to give the little girl (she just turned 13) everything also but this was a blatant slap in the face!!! Plus she was sneaky with the whole situation!!!! The crazy part is at her b-day party her cousins wife said "I thought____ was allergic to dogs, or does he know that you now have one???!!!" I love this girl dearly but what does that say about any other decisions that should be made from here on out at our house???? Plus any credibility with her daughter that I had is out of the window...her dad doesn't like me,,,give me some feedback!!!