Dancing feet,I know what you are going through, but trust me this too will pass, my husband left me ten years ago after 35 years of marriage, and I then found our he had another secret life, and a son who was at that time 9 years old. My children, all grown up,were horrified, and furious,they felt that all they knew about us was a lie. They were angry that I had not confided in them, I think I should have. However ten years on, they have a good relationship with both of us,and their half brother. I am married for the second time, I was 60 just before my wedding, and my ex is married to the mother of his(2nd)son. I can't pretend that it was all plain sailing,but I have come to terms with it and I have now met, and married, the love of my life.
So keep strong and have faith, things will get better,talk to your children you will be surprise at the support and strength they will be able to give you. I agree with magdalene, your husband has demonstrated that you can't trust him, don't presume he will be fair. Good luck.