Is my SIL flirting, what to do? (Update 3)

Hey first of all thanks for some of your suggestions; most of which were straight wrong but the others helped.

So I thought getting drunk for once with my SIL with my wifes; my wife doesnt drink. However things happened sober.

I entered my SILs room to offer her a shake however, i found just out of shower in her towel. She saw my with her side but pretended to be unware.

I found there wasnt any lock on the door and she’s tall so towel only covered her boobs and the back. Her ass, at least the bottom half was totally visible. My instinct was to rush out however, I stayed saying nothing. She even was jiggling her ass just so you i missed. I said hey your shake; she just said yeah keep it there, thanks.

After this she sat beside me on a sofa. I noticed she wasnt wearing bra and the thinest tank top and all of her waist was visible( thats her best part) and bum chums with ribbon out lose. And started talking about the moans she heard of my wife. So i had a deal with her, with every fifa goal i’d fuck my wife. I was 4 fucks out, and my wife isnt exactly loud but walls could be thin at areas. And she heard.

She said “lame couple you guys”. “You shouldve at least thought of me”. I was like “man some signals” In a while she was close and i too made sure to be on loosest boxers. I pack a 7 incher, so i just wanted it be out my boxer sleeve, flaccid. Though it was a tent now.

I had my right hand copped her waist, she came even closer I went inside her tank in a while, and phone in my left hand; soon i brushed past her side boobs almost touching her nips. She had her right hands on my abs; really touching em, especially the crevices of it. And we both had phones on the other hands. My MIL intervened and she had to go.

She pretended as if it was meant to happened but totally ignored the tent. :/