My daughter plays with a imaginary dad?

My kids father's left me while pregnant with our second child. At the time my daughter was 18 months old in June 2008. And in June 2009 I started dating one of my good Guy friends... and I never allowed Herring call him dad even though her dad was gone. But if you ask her who she thinks her dad is.. she says lucas. And we broke up a year ago..and she hasnt seen him nor saw him much whenever were dating because he was in the army. She only saw him 3 times the whole time we were together but it was for a week each time. And so its been a year , and she's playing by herself saying stuff like "daddy I miss you " while on a cell phone.. or she's like "look at this daddy, common come see".. and im not sure how to fix this. Maybe she should go see a psychiatrist. I'm not sure how to tell her she doesn't have a dad. Please only people who are truly going to be of help. Post a answer. Thank you