Everything about what is happening with the sleeping arrangements is problematic and not recommended. A five year old not staying in their bed as a regular practice in our culture isn’t healthy. There are a wide variety of strategies for helping the child stay, but the main thing is to not give in to her discontent and complaining. Of course doing this with compassion is essential, but this is important and necessary.
Although you didn’t mention it I am assuming you and your boyfriend are in a long-term relationship and you have been going out for over a year. If it isn’t then the wisdom of you staying over would need to be questioned, but assuming it is then your boyfriend has to make certain your bedtime together is respected by his daughter. Again, many ways to do this, but him allowing her to punch you without consequences until she gets her way is damaging to everyone.
I would say to give this about a month of effort. If, after that amount of time, there isn’t sufficient progress I’d work with a child psychologist, or other therapist familiar with children and blended families.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral