Why didn't my friend tell her H that she was falling for OM? Well, there are a few reasons that I'm aware of, some I'm I don't doubt are excuses on her part. But below are the ones I would know of.
#1 H's temper - Let me just say he was very verbally abusive and VERY loud about it.
#2 Physical intimidation - My friends H was 6'4" 230lbs (she's 5' and almost 100lbs lighter) he would intentionally intimidate (throws things, comes close to hitting her....like, hitting the wall inches from her head...things like that). So I know she was scared to say something to him for fear of her own safety, especially when she was attracted to OM but nothing had happened. She was also afraid for OM, her H wasn't what you'd call rational.
#3 I know she was trying to fight the attraction as well. This is something she did talk to me about. She was trying very hard to hold her M together....even though in my estimation it was an abusive R. She talked to me about this very shortly before her M completely fell apart (due to the situation below) when the stress became too much and she had to talk to someone.
#4 As far as getting thrown together with the OM....the situation was one where she, her H, and OM were business partners (catering). Her H would often just disappear without saying a word to anyone, leaving my friend and OM alone in the kitchen (which was at her house) for hours on end.
The reason he left her alone with OM I believe was a manipulation on her H's part. My friends H (we found out) was actually having relations with a family friend of theirs who was 16 at the time (apparantly it had been going on since she was 13). Let me just leave it at this....he was a master manipulator of situations and people.
Does that answer your question as far as why my friend didn't say anything?