There may be other wonderful people who she cares about, but you are and always will be unique. Unless, we make children choose between adults, they are generally willing to love and include all of the people who care about them. One of the things that is sometimes difficult for parents is having their child refer to another person as daddy, or mommy. It is important to note that even if your child calls another man, daddy, he isn't you and she clearly knows the difference between the two of you. Think about grandparents.
Many children have two or more grandpas.
There are many things you and your ex-wife can do to support your daughter's relationship with you, even when you are not together. Provide for consistent, frequent time together. Spending frequent and consistent time with your daughter lets her know that Daddys are reliable. It offers an opportunity for your relationship to grow and develop as she matures and changes. It gives her something to look forward to and to hold on to when she is not with you.