I live in Virginia and have discussed health insurance (I have epilepsy) and spousal support with my attorney. There are a few things you should know.

First of all, under Virginia law we have "no-fault" divorces in many cases. However, in cases of infidelity -- that actually is a divorce for cause. You actually need to sue him for divorce to get all the appropriate legal protections you need. You need to get to an attorney (judging by the dates -- I really hope you did). Infidelity is a big no-no in Virginia. It changes the dynamic considerably.

"theanswerguy" was right on the money. The court may order your ex to cover you under his insurance policy after the divorce. Or as mentioned, he may increase your spousal support to allow you to buy COBRA (insurance through his company for a limited time, 18-24 months, I think). And it may go beyond that. It's truly up to the judge. But in a divorce for cause, and given the factors you mentioned (duration of the marriage, you being dependent on his insurance during the marriage, your health circumstances) these things will all weigh in your favor.

You need to be aware that you have a very strong case here and not be afraid to tell a lawyer all that has occurred. You taking him back is not relevant when there is infidelity. But you need to divorce him. I'm sorry to sound so adversarial, I know that's not what you want to hear but that is how you will best protect you and your children's legal rights.