Regardless of the children issues, this couple clearly seem to not put any stock into the value and necessity of poly relationships developing on their own and independently. The fact that she reads all his conversations with the OP indicates that neither of them feel the OP deserves any privacy in relating with this man.
Persephone, I would just stop holding onto any hopes that this can become a romantic relationship for you.
Plunk! Into the friend zone he goes!
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein