Is it wrong to love my sister-in-law?

I live in my brother's house since I had my divorce 2 years ago. She is married to a beautiful woman and with 2 kids. My brother invited me to join them for a threesome about a month after I move here. From that time on, I'm f****** my SIL everytime I have a chance whenever my brother is out or when he is on travel at work. She is hot and h**** and enjoys it too. I dont cheat on my brother because he tells me to look after his wife whenever he goes out of town, like for a week or more. I consider it as a pass since when he is here, he invites me for a 3some from time to time.

During 3some, our s** is tamed. But when my brother is not around, I own her and she is very submissive. I f***** her in the ass, mouth, and tried all the different positions I know on her and she didnt complain and orgasmed everytime. I'm beginning to feel she's my gf, and when bro is on a long travel, I act as her substitute husband. Recently, she is letting me f*** her bareback. And I c** hard in her everytime.

I have several job offers to work in another state but I'm declining it because I fear to live afar. I will miss her. I'm beginning to love this arrangement and if they are both on board, I want this to go on permanently.

But one thing I'm bothered about is how my SIL and bro view this entire affair? My SIL is not a big talker when with me. I'm not sure how she feels about me. But when I kiss her hard, she responds back. One time when I was c******, I told her I love her. She did not answer back but embraced me tight and pulled me harder toward her as I came. The following day, she told me I may not wear condom if I dont want to. I'm a go getter so I did from then on. Is she a case of action speaks louder than words?

It is still a mystery to me how they view me. Am I a disposal 3rd wheel which is just a convenient substitute due to my bro's present work situation? Does SIL have feelings for me or she considers me a mere f*** buddy when bro is out? Do they talk about our s** when he is out of town? Does bro know I'm f****** her bareback? Lots of questions but am afraid to ask.