Try and cut long story short.
At Easter weekend my best friends husband of 10 years walked out on her and their 7 year old daughter to live with, one of my friends "friends". (Another mum at the school, and my friends daughter goes to (the very small < 1 class per year) village school, where this other womans children go....
Anyway he runs his own buisness... (an odd job man painter decorator type guy) and in the past i have employed him.... (you know do the doors in my house, install my bathroom etc etc).
As we (my friend& her DH) lived nearly an hour away when he did work he always stayed over in the spare room as it saved a lot of petrol etc and I didnt mind.
When he stayed we would have dinner etc (JUST have dinner, wanna make that quite clear) but he would go into huge detail about why he was unhappy with my friend and go into great details about there lack of sex life. There was a time when IMO he was definitely trying it on with me (at the time i was single) and i told him straight out not to bother as his wife was my best friend and we just were not going there EVER... end of. He got the message.
(I am 100% sure that i had offered him to come and live with me and be with me he would have jumped at the chance and left her for me)
So anyway i made it crystal clear that there was NO chance ever, that was 3 years ago now, and we have just moved on, & I have never mentioned anything to my friend, or anyone else. NOTHING happened, I didnt see the point in mentioning it... it would only upset people....
A couple of years ago one of my other friends (another of my very best friends actually) was living in my house while hers had major building works, and at some point i got my friends DH round to do some other odd job. (cant remember what, but i dont think it matters)
For whatever reason i wasnt there but my friend who was ataying for a few months was, and she let him in etc and was there while he did whatever odd job it was.
Thought no more about it.
My Mum has also employed him for odd jobs at her house, and again he has done DIY stuff for my mum too. (again thought no more of it)
so (getting to point now) I was on the phone to my other best friend yesturday and said how he had left my friend and their DD etc (they had met at parties and stuff at my house, wernt freinds with each other but knew who the other was through me). Anyway i said how he had just left for this new woman (who he had met by doing odd DIY jobs for her, just the week before) and at the end of the converstaion my friend told me that while it was just the two of them he had gone into far too many details about his relationship with his wife, and suggested that he could get with my friend. (My friend told him no way and that married men with children were not her thing) she only told me this yesturday, I had NO IDEA (But can imagine, it was probably similar as he tried with me)
So TODAY i speak to my mum... and again mentioned that they have split up etc... and 
my MUM reveals that when doing odd DIY jobs for her he has again gone into FAR too much detail, and i get the impression he wanted my Mum too
My friend is devastated that he has left her, and even though he only left 4 weeks ago is already beginning divorce legal stuff etc.
(neither here nor there but he is still being awful and nasty to her and has put her in such a difficult situation, by 1) my friend has to see this other mum (his new woman) twice a day at school drop off and pick up, 2) sometimes HE goes too with her. (all VERY hard on their 7 year old DD as he NEVER EVER was there for her after school, as he was always too busy working)
3) there is just 1 main road in and out of the village and if ever they go anywhere they have to drive past their house. DD see's daddies van and wants to pop in (she often used to go their with her mum) Its all very upsetting for their DD... as she has to see daddies house any time they go anywhere 
The question is do i mention what he did several years ago to me, a couple of years ago to my friend, and just a few months ago to my mum? Or do i just let it be water under the bridge?
(he got with his new woman after he went to fix a door for her and ended up chatting until 2am and the following weekend he just left.... well im sure i know what tha conversation was.... i could have had it too!)
I dont want to cause my friend any more upset, but in a way i feel like she should know that (as far as i can tell) he tried it with EVERY single female!