My sisters husband... UPDATED

PLEASE NO JUDGEMENT 
I have always had feelings for my step sisters husband. He's amazing, gentle, handsome, and just so kind. I've always tried to control my urges but sometimes I slip up and he catches me staring at me and he will smile and just stare back. I am going to my sisters for a little while. About a week or so. And she has now been called in to work a couple nights over night (she is a nurse). I will be sleeping in the room next to theirs. Please give me advice on how to not make a big mistake!! I'm on my way there this morning and I'm so nervous I'm gonna mess up. It's hard to contain my urges around him. Especially knowing we will be alone at night. Please just give me advice! UPDATE: I was already on the road and couldn't go home but I got a hotel instead and only come over when she is home. I guess I should look into some type of therapy when I get back home. I understand why some of you are mad and upset but I'm doing the best that I can. I could of went and did it and not asked for help but I am here asking for help. So thank you everyone.