Your daughter will always love her dad much more then any other man, you can't change that. But you need to sit down with your daughter and explain that your boyfriend will never take the place of her dad, he is to make you happy again.Your daughter could also feel pushed out as you have a new baby too.
Does your daughter have contact with her father?

I have 5 children and 3 of them are from a previous marriage, of which they don't see there father.
My eldest of 8 yrs and gone through all what you describe and now loves her step father very much, all 3 of them even calls him dad.
Things will get better, it just takes time for children to adjust and make sure they aren't going to loose there mum too.