My FIL bought me a nighty, then I fucked him

I lived with my in-laws while my husband was deployed for 11 months.
He and I were in a difficult period...I'd discovered that he had been unfaithful with a old flame from high school just a week before he shipped out. We hadn't time to settle things between us - though he was very upset for ...maybe just for being found out, who knows?
For the final 3 months before he returned I stayed with his parents and little brother (15...and horny as heck!) His dad was sweet to me, but my MIL was not so happy to have me around. I was 18 at the time. We'd married as teens in California. Mom rightfully felt her son and husband were a little too happy to have this blonde California teenager around her house. I'm not unattractive - I've known this since I blossomed around the age of 13. I get hit on a lot!
Anyway to the title of this post...my wardrobe for bed-time and breakfast usually consisted of an old T shirt of my husbands' and my bikini panties. His shirts were long enough so that I could keep my panties from view most of the time. Sometimes I forgot and bent a little too far :-), I could tell this by the looks the males of the house gave me! My FIL poo-pooed his wife for the little remarks she made about my sleep attire...he once said, "the girl is 18 and she can't help being cute! Besides, she's family now!"
About 6 weeks later my MIL went to stay a few days out of State with her ailing mother. I had my 19th birthday coming up.
My FIL asked me what I wanted for my B.D. and I told him I was just grateful of them letting me live with them and saving money for a place of out own, when their son comes home.
A few days later, he came to me and told me to get in the car - he was taking me shopping for some "necessary items"..?
As we pulled up in front of a high-end mall he finally told me what he wanted to purchase for my B.D., "you'll need a new dress for when my son comes home, and in the mean time you really do need to pick out a nighty for your sleep-wear - your MIL is not happy with those T's you're wearing around the house in the evening and at breakfast!"
"Why?", I asked.
"Well dear - sometimes your skippies are showing....and there are two guys in the house who cannot help being males and enjoying these ....moments"
I though, well, OK - guess I'm going to come home with a sack to sleep in! "Let's not excite the men in the house!"
I found a cute dress, just short enough - but not trashy - quick enough. Then we went to the lingerie dept. Dad walked with me through the racks as we look over the selection. I found two that I would grudgingly wear ...and took them to the fitting rooms area. Pop saw that I wasn't thrilled as I walked away to try them on - he said, "let me see what I can come up with, honey!"
In a few minutes he came outside my fitting room and said, "here, try these on and see what you think." I cracked the door and he handed them in.
"Woah!"...all 3 were super sheer, short, slit up the sides and expensive! The little sheer string panties on the hangers as part of the set were just plain "R" rated, too! They barely covered my bush in front and left a lot of my bottom in view - plus my dark blonde triangle and my butt crack were still pretty visible!
I stood there looking at myself in the mirror...and didn't know what to think. I was taking too long apparently. There was a knock on the door, "Are you OK in there? Have you made up your mind? Don't worry about the price - it's my present to you from your MIL and I!" (I'm thinking...."really - MIL you'd love me in one of these!?")

I said, "I can't make up my mind. They're all so pretty....and frankly - very sexy!"
He said, "Yeah, I thought so, too!" and laughed.
I stalled longer- uncertain which color I looked best in...
Finally, he tapped on the door, "do you want to show them to me? I'm a guy and I can help you with which you look good in. I won't gawk or get weird - I'm old enough to be your father for Pete's sake. What do you think? ..."
I wasn't sure what to think. They were expensive - more than we couold afford - and he was buying them for me - and Hell, he WAS as old as my dad! So, I opened the door and told him to come in.
Now I'm not big busted - but my B cup breasts are blessed with really cute and pouty nipple. My husband loves my furry bush - so I don't do more than a trim to keep it in my bikini bottoms for swimming. And my girl attributes are on full display in these suddenly very sheer nighties! Sheer?...I could tell by the expression on his face that he was seeing an awful lot of me - and enjoying every bit of it...ME! He said this lone looked great! having me turn slowly so he could look at my 18 yr old butt!
Then he said "let's see how you look in the others!"
He was enjoying this WAY too much!
I said Pops, you need to turn around while I get out of this!
He reluctantly did.
Now I am in a small, suddenly ever-heated little fitting booth with my FIL and I'm stripping naked to try these nighties on! Why wouldn't I be freaking a bit. This was awkward....and dammit, sexy, too! My FIL is a nice looking man! and he's liking what he's seeing!
I noticed that both of us were blushing by the time we walked out of that little booth! And I'm pretty certain I spotted a little tent in his slacks - and I know I was more than normally moist down there!
So....this is all the back-story to how I ended up in bed with my FIL later that night. After thrashing around in my bed for like 2 hours, horny...scared, horny...
I put on the color he liked best and walked softly into he room and stood by his bed.. I knew he could see all of me in the streetlight. My nipples were aching and my puss was wet. I stood there wondering if I was being super stupid...when he pulled back the covers and invited me into his bed. We said hardly a word - but we knew how to communicate our needs to each other.
He was large, thick and a nice length. I cautioned him to be gentle with me, as my "cunt has not had anything larger than my fingers in me for many months!" He was gentle....it hurt. but a nice hurt. He ate me to get things started. I sucked his beautiful cock but he refused to cum in my mouth - even though I told him it would be OK. Such a gentleman. We came and slept and came until mid morning. I had to pee and he made coffee. Then he fucked me over the breakfast table. We carried on like kids for 3 days - until my MIL and BIL returned.
We still have a very special relationship....though nothing naughty has happened since those crazy 3 days! No one knows.....I sure never told his son! And I doubt MIL would keep him in the house if she knew!