Hye,
In my humble opinion, I would suggest that you try to meet up with the girl he is having affair with. Not with any comfrontation but in a gentle way. Try to tell her that what she is doing is ruining not only your life but your children as well.
I know that many China girls here are after our men for money only but in remote possibility, maybe she could understand your situation and leave her relationship.
On the other hand, maybe you should be looking at the reason(s) why your husband is having affair as well because that is the root of the problem and work out from there since he have cheated on other different girls before.
This could be because of his work (maybe he need to meet alot of girls), his friends (maybe most of his friends are playboys) or lack of private time with you (long or odd working hours) or maybe because he is bored with his sexual life.
If he is just bored with his sexual life with you (possibly as you married early), try to spice up the relationship by doing something special during intercause. I understand that this would be difficult especially after a big fight, but try to give in for the sake of the relationship and children.
Finding an affair for yourself is a double sided sword which maybe make it better (because you could in a way could be happy and he would start to feel jealous) or maybe make it worst (if he gets upset over it).
I'm no expert but try to think about it. Afterall you would be fighting to keep your family in the end :)