Here is what I have...Feel free to chime in on what needs to be changed since I won't be sending it until tomorrow.
Dear H,
Until I'm satisfied that both boys are receiving equal attention from you and one is no longer being purposefully slighted and hurt, I don't feel comfortable with this arrangment.
I feel hurt and angry when you chose to see C over N. While I wouldn't keep either from you, you need to know that N also misses you and will feel devastated if you only see C.
As their Father both the boys need to spend time with you. You know how I feel about the boys being around M (OW) and letting the boys around your mistress is disrespectful to them, me and reflects poorly on you as a man and Father.
If you won't agree to to keeping them away from her then I cannot condone them spending time with you.
In the future, I would appreciate you talking to me and not C about him visiting you.
If you continue to pick C over N, then the next step will be custody arrangements filed in court.
Serenity
May All Who Seek To Take My Life Be Put To Shame And Confusion; May All Who Desire My Ruin Be Turned Back In Disgrace. ~Psalm 40:14~