So just to start off this is my wife's older bro's wife. She is about 8 years older than both of us but have always considered her attractive and as she got older developed into a proper MILF (mid-30s). I'll call her Anna here for convenience.

So we were doing the usual family thing on new years eve and this year we are over at my in-laws where we'll often spend the night afterwards as we'll all drink into the small hours. I know Anne and are husband are having issues and it's a bit of a tense evening as a result, as we're all trying to ignore it and avoid bringing up any subjects that could trigger an argument.

Her husband is on the whiskey and is getting hammered to a point that by the end of the night he is slurring his words and can barely stay awake. Anna appears a bit flirty with me but nothing too obvious, sitting close, very chatty with me in particular which is unusual for her.

It's going on 3am before we start making our way up stairs to our respective rooms. My wife and I are in separate rooms simple due to both rooms only having single beds, her in her old room and me in one of the small spares (in-laws home isn't massive). Anna and her husband have a room with a double bed and both retire to their room as well as say our goodnights.

I am in bed about 15 mins max when the door opens, I am expecting to see my wife but it's Anna instead...she asks if I'm awake and explains her husband is snoring amd taking up all the bed so she can't sleep and asks if she can come in next to me.

She obviously hears the hesitation in my voice as I start to fumble out a response, so interrupts me with something to the effect, "don't worry I won't hog all the covers, as she walks over to the bed and climbs in.

And mind you this bed is very small and I am basically forced to push by back against the wall and lie onto my side. She says goodnight, and try to sleep, very confused but assuming she's just a bit drunk so not properly thinking about how this looks.

After about 10 mins I reckon I am just drifting , though probably only half asleep when I feel something rubbing into my crotch area.

I open my eyes, still a bleary eyed and try to discern what's going on, only to find Anna is grinding her ass into my crotch. I am stunned and try to get my bearings to make sure I am seeing things right. Then I hear her stifled moans, and I can't be certain because it was so dark but I think she was touching herself as well.

I guess she sensed me moving behind her so turns her to look at me. I placed my hand on her hip and pulled her into my closer...from there things just escalated into easily the best sex of my life.

After we done she snuck back out. No appears to be any the wiser though my in-laws did reference the following week the state of the bed sheets, and I had to basically pretend I'd be very sweaty that right, though they probably think I pissed the bed a bit

While nothing else has happened since, she's recently started texting me out of the blue...