My Sister

I watch porn mainly girls doing deep throat, when i got a surprise this girl was almost my sisters twin with same hair style and build, what happened was i ejaculated in my pants i really creamed my self i had to change underwear and pants , i****t is something i have never thought about her in a sexual way even though she very fit and attractive, now i can not get the image of her doing the same for me, but how to set about a relationship, i get an uncontrollable erection when she is around, she has noticed it