I replied in your other thread, so my take on your situation is there. But in regard to what you're asking here, all I feel I can say is this: Don't try to manage his other relationships, just manage your own. Whatever he tells her or not isn't up to you.
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