I am feeling a little guilty these days. I wish the kids had a mother to look after them. Of course I do not want to get in a relationship for the wrong reasons either. How do you handle the guilt?
What will be, will be. You can't look at it that way. They have a loving father and he is doing the best he can for them. If you find someone you wish to be with, then that's fine. Just be up front with the kids that this may not be a "forever" situation and you are just dating.
Families come in all shapes and sizes, you are there for your kids and give them the love they need. Is there someone, a female relative, that might help with fill the void of not having a mom around?