I second the cruel remark.
have you ever been told that you were unwanted?
that is a harsh blow to anyone's self esteem,let alone a child's.
It would be even worse coming from a mother.
My advice would be to leave the unwanted comment out and maybe say that the father loves you,he just wasn't ready to be a dad or something along those lines.
You should never(EVER) talk bad about the other parent in front of a child regardless of whether the child even knows the parent or not.
And about the new bf on the birth certificate,I think I would prefer to have noone on the birth certificate.I would never put somebody on my son's certificate that wasn't his biological dad.
And there is a perk to not putting him on,he isn't legally bound to you,if he stays it means he stays because he wants to not because he has any obligations to the child.