I Slept With My Brother-In-Law By Mistake”

I had sex with my brother-in-law by mistake. In the dark I thought he was my husband.
I’m 29, my husband’s 31. His parents held a family party for his niece’s 18th birthday last weekend.
Everyone was there, including my husband’s brother who was home from working away in Saudi. He’s 36.
We all get on well and there was plenty of alcohol and food. It was a nice party and we carried on drinking and dancing into the small hours.
My husband went up to bed before me and said he’d be waiting for me. I followed him up 20 minutes later. I got into bed feeling frisky and we ended up having sex.
I woke up a couple of hours later and sat up to get a drink of water. I pulled back the curtain to let some light in through the window from the street lamp right outside the bedroom.
I looked round and got the shock of my life when I realised I was in bed with the wrong man. The man beside me was my husband’s brother. I’d gone into the wrong bedroom and I guess my brother-in-law thought it was his lucky day. We had all had a lot to drink.
I ran to the right bedroom and crawled into bed with my husband who was fast asleep. Then I realised I’d left my underwear in the other room, so I sneaked back.
My brother-in-law was stirring so I hissed that we must keep quiet about what had happened. He just said, “Whatever.”
He’s flown back to Saudi now but I don’t know whether to admit everything to my husband. If this comes out I’ll lose a man I love more than anything and cause family ructions