My slutty sister

I’d never been too much into incest until I found out my sister is a straight up slut a couple of months ago. I’m super into couples, hotwives, gangbangs, etc, so I often check out fetlife and other similar sites/apps. I’m your normal clean cut, socially conservative, professional type so I’m very discreet about my sexual depravities and usually seek out similar situations. I’ve been talking to this milf I had seen post a few times, she’s super into gangbangs and creampies from random strangers, and love’s anonymous meetups. We never sent face pics just some nasty vids/pics. Fast forward to Father’s Day when my sister hosted a cookout at her new house. I went to use the master bathroom cause the other one was occupied and immediately noticed a mirror and armoire that was super familiar…then it clicked…it was in the background of the kinky, depraved, cumslut I had been talking to that was also my sister. I immediately got hard as a rock and wondered if I should do anything, she does have a huge cnc fantasy so I thought about just pushing her against a wall and emptying my balls in her but I got nervous that she’d draw the line at fucking her own brother. Now im super conflicted on what to do, should I tell Her or just show up and creampie her while she’s blindfolded like we’ve talked about doing several times. I can’t stop Thinking about her and how taboo the whole situation is.