My sister-in-law (43) is my best friends sister (44)

My sister-in-law (43) is my best friends sister (44) and they kind of look alike, I can’t lie and say that I’m never sexually attracted to her but I’m also super afraid of ruining my marriage, I know I should just see her as a sister and not some real life Harley Quinn (I mean she’s no Margot Robbie though) but it’s kind of hard, I can’t see myself raping her or anything but some real boundaries were crossed on Christmas, I don’t think I’ve felt that way about a woman since I first saw my now wife (43) back in middle school, I know this is wrong.