Sharing Girlfriends With My Son

My son and i lived together in an apartment. When he was around 20 years i was 40 and we looked about the same. Same body type (both working out now and then), same height, same kind of clothes. And we looked at the same type of women.
He, off course, had less issues with finding one night stands and took a girl home every now and then.

So, one day, he had this girl in his room and after she went to the toilet, she took the wrong door and i woke up by feeling someone sliding into my bed. I didn't realize what was going
on till she started to kiss me, smelling a bit of alcohol, her hand on my responding dick and a soft 'hey, are you getting hard already, lets do round 2'. She asked me to get a condom from my nightstand, which i quickly did, then she got on top of me, her hand moving my dick to her pussy and she started to ride me.
I hadn't said a thing, it was just her riding me, my hands all over her body, feeling her nice
boobies and ass. She was riding me hard, moaning softly in my ears to fill her, to cum, which i happily did. She felt me spasm, then moved her hips to my face and let me eat her.
She tasted good, moaned loud when she came then got into bed with me and fell asleep.
I got out of bed, went to the toilet and thought about this. I entered my sons room,
he had fallen asleep but when i shake him a bit he woke up. Son, something happened, i started.
Shit dad, did you really fuck that girl? Son already knew, we shortly talked about it and he went to my room, slept with her in my bed while i slept in his bed.

Next morning they came down, (son later told me they fucked that morning again), breakfast like nothing happened. As soon as she left our house, he told me he thought it was pretty horny we shared her like that and we talked about how to do that again.

So, for a few years, when one of had a one night stand, after sex one of us goes to the toilet,
the other goes into the room with the girl for a second round of fun. Keeping the lights of,
most girls (and women i took home) didn't notice and we got plenty of pussy to share.
Most girls didn't notice and the few who found out had a laugh (and 2 girls were mad and walked out the door). Wished son would still live with me