Been Playing House with My Husband's Sister...

So here I am, married for twenty years now. We’ve had ups and downs but we always seem to find our way back to each other. Last month though... wow, this is going to sound really messed up. But it’s been eating at me ever since. My wife has a sister who moved in with us six months ago because she lost her job and needed some time to get on her feet. Her name is Carol and I’ve always liked her, she’s easy-going, funny, and very attractive in an understated way. At first it was fine; we all got along great. But over time... something shifted. I started noticing little things that made me uncomfortable. Like how my wife would catch us looking at each other across the room sometimes and give her this knowing smile. Carol always looked away quickly but it felt like she knew exactly what that smile meant... I mean, we were flirting of course, just harmless playful banter really... I think? One night after a few glasses of wine my wife had to go to bed early because of work the next day and I was still up watching TV. Carol came in for water and when she walked by I felt her leg brush against mine on purpose. She whispered something about me being handsome before heading off to her room. I couldn’t shake that feeling though. One night, after my wife had fallen asleep and Carol was home alone in her room with just a blanket over herself, I knocked... and she let me in. We ended up talking for hours but it got more intense as the night went on... She told me things about herself no one else knew. Things that made me feel closer to her than anyone ever has before, maybe even my own wife? It’s such a weird feeling. I still don’t know what it means... and now I’m really confused. So there you have it... the whole story. Feel free not to take any sides or whatever, honestly I just needed to get this out in case it ever comes up again and ruins everything. This is my life right now though, even if it makes no sense. ...