Been Hooking Up With My Best Friend's Partner

So I've been seeing my best friend's partner for like, weeks now. We met at some party and hit it off right away. Knew from the start she was with someone else, but figured why not? Everyone's doing it these days anyway, right? We just have this connection that feels so right, even though it's complicated. Feels good to be wanted by a woman like her, you know? I'm sure my bestie would flip if she knew, but whatever, she'll get over it.