Heartfelt you show a willingness to be honest about difficult things.

It is good for you to do this, regardless of your h reaction because radical honesty makes couples understand each other better. It is not surprising he doesnt understand the danger when you gloss over so much. Telling yourself 'oh it wont help anyway' is not productive. If you make yourself more transparent and accountable, your state of mind will improve.

Maybe give your phone to your h for a while until the number can be changed? Or if he is not keen on NC letter, ask if he could he possibly send a text back to OM which says, 'Oh its heartfelt's hubby here. I have her phone today, she lends it to me sometimes. She asked me to check something when I saw your message. Thought to myself thats funny I dont remember her singing that song - are you sure you didnt mean someone else?'

This 'friend' may then get the message that your phone is not a good way to get in touch as your h has free access to it. He will aso be (deservedly) embarrassed in front of his friend as to what a little sneak he is.

If (as you say) your h wants YOU to be accountable and to put a stop to things - you cant really do better than that can you?