I dont know of any books, but Ill tell you how I handled our situation. I was on your SO's side, so I dont know if this will help at all.
I was 19 when I met my now dh. At the time, his dd was 8 months old and he didnt have her full time. I love his dd (turned 8 in July) like my own, but still different. Its hard because she isnt being brought up with the same values or in the same type of household that we bring up our own kids when she is at her moms. It makes it hard to transition when she comes for the summer or her other school vacations. But Im getting off the subject.
Im assuming you have full custody of your dd here. Going to the "next level" is hard. If you and your SO are committed to making your relationship work and are talking or have talked about marriage (again, I am assuming marriage is not the next level you are referring to), he needs to think hard about the impact this change will have on HIM. Does he want to have a role in parenting? Does your dd get along with and trust him? Does he trust her? If it all works and you get married, is he ready to play a father figure? Are your discipline styles the same?
Another thing that needs to be discussed is what kind of life he wants to have. Does he want to have to option to make a decision at 6PM Friday night to go out with his buddies without having to "okay" it through you?
You both also need to clearly state your intentions in the relationship. Even if you think they are already known, this is a big step and things may be different because of it. Do you have different expectations?
Like I said, Im not sure what the next step is for you. In my situation, the next step was living together. For others, it might be marriage and for others, it might be exclusivity.
There are different things I would say for different situations.
If you want to, feel free to PM me. This is a hard decision to make, I know.