Attraction Towards My Sister In Law

Hi all i am 22 and i am sexually attracted towards my own sister in law (brother's wife). She is 28 and we both are close to each other. For the past 10 months i am getting attracted towards. And now for the past 3 months we started having sex whenever my bro is not in the house. We at least have sex once in 3 days and my bro don't know about this. And now she just become nude every time we both are alone at home and also tell me to do the same. Some times my bro is out of town for work and during that time she calls me to her bedroom. Whenever I am having my food she comes and make me hard. Now she wants to have me and my bro at same time. She had even convinced my bro to have another person on bed with them but my bro don't know that it's me she is talking about.
Now i am in a big dilemma of what to do. I don't know how will my brother react when he comes to know about all this.