Last weekend whilst visiting my mother in laws with my new wife, I caught them kissing in the kitchen. Not your everyday family kiss, but a full on passionate tongue swapping kiss, and they were both feeling each other up.
I've always known they are close and I kind of suspected they'd maybe done something together in the past. This is from daft things my wife had told me as we dated (I thought her mom had in some way taught her about masturbation). But I never for one minute thought they'd had real lesbian sex.

Watching for some amount of time, they actually began to finger fuck each other after putting their respective hands up one another's skirts. Thinking I might get caught watching, I eventually darted back out to where I'd ben smoking in the back yard. And was finishing off another cigarette with ahuge boner in my shorts, when my wife walked up to me. She asked me had I just been inside. I lied and told her I'd been outside the whole time. She actually looked a bit glum that I hadn't been inside and looked down at my cock bulge. Asking if I was sure I hadn't been in, I again said no. looking directy into my eyes my own wife said "Yeh, right sure". Walking back in she clasped my hand and made me follow her.

My mother in law was sat at the kitchen table when we walked in, looking very flushed. Smiling at me she asked if we were staying for our evening meal. I was about to say no, but my wife said "Yeh I'd like seconds". We'd not even ate whilst we were there so her comment was so out of context, if I hadn't seen them having sex. And they both laughed one of those knowing laughs. Nothing else happened that I'm aware of that evening, but then again I did fall asleep after our evening meal and they were upstairs when I awoke.

We're back at my mother in laws again next weekend. Only my wife has said we're staying over, something we've never done before. I'm not sure what to make of all this, but it was sure damn horny watching them make out.