I am glad you mistress is providing you with the love and support that anyone should expect from a marriage or romantic partnership.
I also can relate to feeling extremely bonded to a dear child and putting that love before all other loves-- love for yourself, love for your mistress.
Or... is she your mistress? You say you've "met" her. Are you lovers?
I doubt many of us here know the precise legal ramifications of having a wife from a distant country who might return with your child, were you to break up.
My only advice is to get a lawyer now and find out from them what your legal rights are around custody. I know in many states, if a couple breaks up and there is a shared custody arrangement, partners can be forced to stay in the same state, much less leave the country and move to the other side of the world.
Of course, the fact you've been infidelitous sexually might not weigh in your favor. Any evidence of your cheating (should your wife suspect you are), texts, computer messages, credit card bills, etc, can be used against you.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
There's no lying in polyamory!
I'm a 58 year old woman with 2 partners:
miss pixi, my live-in gf, 36 (together since Jan '09)
Ginger, bf, 61, married, lives nearby (together since Jan '12)