I have a friend in Australia and she seduced - or was seduced by - her son's "friend". The story may not tick all the checkboxes for BFMM, but bear with me, it's a hot story.
This took place about fifteen years ago, in a rather posh suburb of a big Australian city. My friend and her family had a nice big house with a big garden and a swimming pool, so it was a natural place for the kids and their friends to hang out. Her son and his friends were all around 14 at the time, so naturally most of them were full of hormones and puberty.
Some of the boys were more cocky than the others and flirted non-stop with my friend. They wore speedos rather than board shorts in order to show off their maturing cocks, and apparently they were all quite impressive.
My friend liked to hang out at the pool with the boys, and naturally got a lot of attention. She was already known as a MILF among the boys, and of course the son was teased endlessly by his mates about what they'd like to do with her. She thrived on all the attention and compliments she was getting, and responded by appearing in ever smaller and sexier bikinis when cavorting round the pool. And when they flirted with her, she flirted right back. I think that her son was deeply embarassed by all this, though I never got him to comment on it.
One of the cocky youngsters was very forward, and was the only one who had the confidence to touch her, like patting her ass, or holding her while playing in the pool. He also had the most well-filled speedos, a fact that my friend really appreciated.
This kept building, and one day my friend pulled the cocky one aside, and told him that if he came by the next day he might get lucky. And so the affair started.
Apparently he was a very competent lover, and knew how to put his big cock to good use when he fucked her. After some time the reason for his competence was revealed: He had already been fucking his sister for a while. I don't know how long it took, but eventually his sister joined in and they continued as a threesome.
I haven't got many details, but apparently their favourite position was the boy fucking my friend from behind, while she had her face between the sister's thighs, lick and sucking. A remark by the sister gives an impression of the intensity of the fucking: "Hey, take it easy on her, she almost bit my clit off."
The boy liked to piss off my friend's son by telling him about fucking his mom, and how hot she was. The son at first thought he was bullshitting, but one day he snuck into the house and both heard and saw them fucking, an intense experience that gave him fapping material for many years.
The son and mom's lover weren't really friends. They hung out because they were in the same class at school. Loverboy liked to mess with the son, telling him about fucking his mom, so the son thought of him as an arrogant prick and saw him more and more as a bully.
The affair lasted a number of months, until the boy and his sister moved away.
So, mothers who are tempted to have an affair with her son's friends or bullies, or mother's who are already fucking their young lovers, or bullies trying to seduce that hot MILF in your neighborhood, it does happen, it is possible, and you're not alone.