Update #10
I did get some sleep, but not until late - I don't feel a single regret, either. I had to focus as bit at first to hear anything, which I assume was just him trying to convince her. However, once the faint sighs and moans started, it didn't take long for the bed to actually rock. Maybe a few minutes after that, I actually started to hear my mother's actual moans and squeals.
The entire time I was laying in bed, I got to hear her actually lose it - she did scream his name once or twice, but it was those guttural growls when she came, that did the trick. I did get to hear him use my name during their fucj session, but more as a "You like that? You like being fucked with *** in the next room?" She didn't even hesitate to yes, and that she didn't want him to stop.
As per our bet, it seems I have a new dad, now. I mean, that's not bad, right? My mother seems to love spending time with my new dad, and she gets to be fucked into satisfaction. I'm happy for them.