Put the child first. One way to be a really good parent is to model good behavior, even the behavior needed to fix what is going wrong---and if you are your best self, you will be the best for your child. It might not be bad for you and the boyfriend to separate a while. How involved is he in child care? Does he share your concerns and want to be the best dad he can be? If yes, you can work together, with some help---if he has disengaged...
Always let your child know you love her, ...and when needed, that you are not perfect but always there for her. There are two parents here, and one child....why are you putting it all on you/about you in a sense?