My 19yr old wife fucked my Dad - they think I don't know

While I was in the Army - stationed over-seas, my 19 yr old wife stayed with my parents and 16 yr old brother for several weeks towards the END of my deployment.
The point being - that my sexy teenage wife had been without our very rowdy marital sex for 8 months - and she was feeling it!
She did confide in letters to me that she was getting really sexually frustrated, and that her hairbrush handle and her pillow were no longer satisfying her needs.....and she hinted that my dad was "looking better and better!"
I knew she was just horny and was trying to wind me up - so I told her, "hey, if the situation presents itself....!"
And later I added, that as a kid I'd often heard my mom getting thoroughly fucked by my Dad - so, "I think he could - and would enjoy - taking care of a teenager's needs" - for sure!
So, we're both throwing sexy stuff at each other - sexually teasing each other - which was probably not too smart on my end.

Because:
A few months after I'd returned - and my very tipsy young wife (OK she was drunk) was riding merrily away on top of me, in reverse cowgirl, as I enjoyed the sight of her teenage butt hole and ass cheeks! ....she drunkenly let slip this remark:
"Gawd - how your Dad loved it when I rode him like this! It was his favorite way to fuck me - with his hands squeezing the shit our of my poor butt. He always made me wet his thumb in my mouth before he went playing with my butt hole!"

I exploded into her with this remark!.....and then lay there trying to decide how I felt about this revelation! I had always suspected something - after her teasing letter writing involving my Dad came to a stop. 'They tried, got caught'...what?

She was on the pill, Dad was a good fuck, no harm done, the family relationship seems back to normal - and 'safe' - because my parents moved in retirement back to Europe.
Maybe some night in bed while she's happily fucking away on top of me I'll let slip that I know all about what she revealed to me one drunken night!
Meanwhile - I keep having explosive cums whenever it pops into my head while we're having sex!
Probably a sick thing to do....but it is sexy!