Is it normal to be sexually obsessed with my sister in ly

My wife is very attractive and we have a very good sex life. Her younger sister is also gorgeous but she is more sexy and daring and flirtatious. She often teases me wearing loose blouses without a bra whenever I go there. She once asked me to please get her purse out her gym bag as she was busy with her sister. I did and she on purpose left a few of her skimpy sheer panties there that were used and had her scent and creamy pussyjuice stains. I did what most men would do I took them and went to sniff her scent and taste her love juice. I came so quickly as I was so aroused as this would be the closest I’d get to her pussy. I cannot get her out my mind even wen my wife and have sex. I very curious is she like her sister in bed. What her pussy looks like if her cubic hairs are the same color Texture. Does she shave it clean like my wife. If she gets as wet and excited in bed. I’m basically comparing the two sisters and the lust is that it’s something I cannot and should not indulge in. I’m very tempted to send her naughty text messages to see if she is eager To be fuck buddies that and just have raw passionate sex with no emotional attachments