Let's talk about what is at the core of the issue -- how you have approached dating and how that has affected your children.
I believe your approach and how you integrate dating into your life and the life of your children greatly impacts how well they might adjust to an eventual marriage and step family situation.
After my late husband died, my first thought was about my children. Somehow I knew that very far in the future that I would be okay and even possibly find another mate. My children were another matter; they had lost their father and would never have another one. That is not to say that they couldn't have a "father-like" figure or some other male role model from whom they could learn and eventually emulate.
The very first piece of therapeutic advice I received was the best. When I asked what I could do for my children, the counselor told me that they would follow my lead. If I chose to "recover" then they would too. If I stayed mad at the world, depressed, etc., they would too. So, a week after my late husband died, I made a conscious decision that I was going to be proactive in my grief work and do everything within my power to show my children how to gracefully move from darkness to light. My energies were focused on them, and we did most out-of-school activities together. It was about two years after the death of their father that they finally said to me, "Why don't you go out and have some fun with your own friends!"
What I had accomplished by intensively focusing on my children in this way was that they felt safe again in the very unsafe world they experienced after their father's death.
During this time, I also conveyed to them what I was doing to keep myself healthy so they didn't have to worry about me getting sick. I always let them know where I was and when I would return. If I were even a minute late, I called to let them know. Due to my courteous behavior, they returned the favor. Even when they were older and in their twenties, I always got a phone call if they were to be late.
When a child feels secure, it is easier for him/her to understand the concept of the ever expanding heart, which is that there is room in there for lots of people. Moreover, simply because someone new comes into your life, it does not mean the old residents get kicked out. Love simply creates more love. It is to be shared, and there is always enough to go around!
This is a foundational issue in building a successful step family because jealousy between the children of the different spouses or jealousy over a new wife or husband can easily arise.
Giving your children enough time to heal their hearts before asking them to open it up to welcome someone new is also an excellent reason not to jump into dating too soon after a death or divorce. Households must be stabilized before they are able to cope with more change.