We Are Both Sleeping With Her

I am 18 and my mate are both taking it in turns to fuck a 25 year old woman.
We go round on different days.
She is on her own with a small child.
All our mates think it’s great that we are getting a piece of older ass.
She is still married, but he walked out.
I quite like her, but my mate who is 16 ( I know it’s illegal) keeps boasting about what they do in bed.
She would be horrified if she knew that he was saying these things.
He says that she has sucked his cock, but she hasn’t done that to me.
Should I tell her about him boasting?
I am worried about her reputation