The difference between the cost of his insurance for just him, and for the both of you is nothing compared to what it will cost you to go out and get insurance on your own.

Trying to get you off of his insurance during a separation clearly shows that he isn't in any way committed to trying to work things out.

Speak to a lawyer, if you file for divorce it would likely prevent him from removing you from his insurance until the divorce is final. And just because you file for divorce doesn't mean you have to go through with it.

You NEED to start to take steps to protect yourself, clearly he is positioning himself for a divorce, self protection needs to be a priority for you.