My Sister-IL is pregnant and I have no idea what to do

Had an arranged marriage last year, I tied the knot with Priya, a beautiful Punjabi girl from Delhi. She has an elder sister-in-law, Riya, who's mute and looks exactly like her with all the features, has always caught my eye with her shy, cute smile. that lights up whenever I'm around, way more than Priya's distant vibe.

Riya moved into our flat a few months back to help with chores while Priya focused on her job. Tbh my wife had been rejecting my advances for weeks so one day i was very horny and made up my mind to demand sex. I burst through the door, saw what I thought was Priya in the dim kitchen light wearing her loose salwar kameez, grabbed her wrists, pinned her against the counter, pulled down her pants and had rough sex without the rubber .After few minutes, had an ejaculation. It wasn't until she turned with that mute hesitation, that horror hit me: it was Riya.

Panicking, I told her to take an i-Pill immediately, swearing secrecy, but now, weeks later, Priya drops the bomb she's pregnant with her boyfriend and is quite excited but I am shattered. How do I confess the truth without breaking my marriage ? (Pata hai aaj kya hua)