This is my second marriage. No kids from first marriage. I often find myself thinking of my first Husband and wondering if things would have been different if we had children. Maybe we might still be together. Is it ok for me to feel like this?

This is not very good for your current husband thing as past, happen had happen. If your first husband with you have a good life, why you choose divorce in the first place? This not fare to your second husband, if now you have a lovely life why still thinking the past. Enjoy your life now maybe this time you choose the correct guy?