HELP... am I over-reacting?

Do you want to divorce him?
You certainly have every reason to! If not, give him an ultimatum, to cut all contact or lose his marriage to you.If he is willing to lose you, then you have your answer.
An awful situation for you, but you must decide soon what to do.?

About the children... I don't think it's necessarily their business. I don't think you should tell them unless you wish to. And certainly don't tell them because you hope they'll gang up on him or get him to give up the ow.

I see that caduvovo says the ac of the lady she knows "were furious" that their mum hadn't told them about their dad's infidelity. But, imo, she didn't owe them this information. It was between her and him. It was bound to come out, eventually, surely. But she had a right to tell it when she saw fit. So did he, imo, but not as much since he was the perpetrator.

Thank you all for your comments and support. Close family support isn't available. Both our families are in the UK and our sons are in Australia with enough problems of their own. He is flying to Guangzhou on Thursday to spend a long weekend with her. I am going to Sydney to be with my grandchildren. I can't stay home alone. I have told him I won't live with three of us in this marriage. I am hoping he will have the balls to end it but I am not holding my breath

For me, this would be a deal breaker kiwi . He's showing you zero respect and for me personally, I wouldn't be able to continue. But whatever you decide, I wish you well.

If nothing else you need to get your financial situation on a firm legal footing while you think the problem through.

If your husband would do this to you, he is just as likely to upsticks with all the family money and savings to move to China and spend it all on his floozy, leaving you in poverty and possibly homeless

Do not say to yourself, which I rather get the feeling you are at the moment, that he may have found himself a floozy, but he wouldn't walk off with all the money/leave me permanently for her/it will all blow over he loves his family too much.

A short time ago you would have said he would never in a lifetime go off with some floozy - but he has, so at least protect yourself financially and do not keep putting it off in hope that you will wake one morning and find it was an awful dream. It isn't and the sooner you grit your teeth and face up to it the better.