Reddit reviews The Smart Stepdad: Steps To Help You Succeed

Smart Stepfamily also touches on this topic quite a bit. Lots of side bars and things that speak to how to respond/react/etc if one parent has passed away. (It also talks about how to respect what was before you even if both parents are still living, IIRC.) Also, I know Smart Stepmom discusses this (reading currently) and I would guess Smart Stepdad does too.

Ron Deal's book: The Smart StepDad

As far as advice for you: take your time. Date to establish trust. If you won't trust your BF with your child, then do not marry him. Part of what you'll have to learn to do as a spouse will be to shift your priority from your child to your marriage. That is a step that many people in first marriages struggle with, so its not surprising that it is even more difficult for bio parents in a blended situation to struggle with it. But failing to put the marriage in the proper place in priorities is one of the leading causes of blended family divorces.

For him, he needs to not try to take the place of her Dad, but still be a trusted parental figure. He'll need to be patient, kind, and above all, keep a long term perspective about the parenting. Your daughter will control the pace at which she chooses to connect with him. Not you or him.

He'll also need to learn to be your support and confidant. The two of you as a united front as parents will model for your daughter what a healthy relationship is supposed to look like. That's the best gift you can give her as a mother. It is your relationship with your BF/husband that she will use as her model when it comes to her future relationships. Parenting is more caught than taught.