A Complicated Dynamic at Home

I've always been close with my older sister's husband, let's call him Alex. He's in his late thirties and has always played a fatherly role for me since I was young, teaching me how to drive, helping me get into college, lending me money when I needed it. But our relationship took an unexpected turn during the pandemic. With everyone stuck at home, we spent more time together than ever before. One night, after drinking too much wine, we ended up in a situation that felt wrong yet oddly right, Alex was comforting me and things escalated beyond platonic affection. We both agreed it was a one-time thing, but the frequency of these encounters increased, each time feeling like an attempt to mend old wounds from our childhoods, or maybe just to fill the void left by loneliness. I've been avoiding looking into my feelings because I know this isn't normal and that Alex's wife, my sister, deserves better. She has no idea what's going on between us, but every time we're caught in a moment of intimacy, it feels like the weight of our secret crushes is suffocating me. I find myself torn between the guilt and the intense connection. I worry about how this will affect my relationship with both Alex and my sister if she ever finds out. It's not something I want to admit even to myself, let alone others. But every day feels like a delicate balancing act between our secret love affairs and their perfect marriage.