Children have their own set of needs. Don't add yours to theirs. Stay focused on being the parent. It's all about them. You had your time pre-divorce. Once the papers are signed, start living your new life.
The politics of divorce often come into play when it's time to have a wedding. Even if your parents have been happily apart for many years, the traditions surrounding weddings force everybody involved to declare, more or less, their position in life relative to the bride and groom.
He's going to be one heck of a stepdad!
13-year-olds are reluctant to confide in their parents. One of the benefits of being a "bonus parent" is that you can act as a sounding board for your stepdaughter to talk freely about the things she's struggling to sort out.
When you fell in love with your husband, I am sure you had great hopes of creating a happy family that included both of your children, but as you are discovering, blending a family is often easier said than done.
My mother and I grew up in divorced homes, and we endured the experience of having both stepmothers and stepfathers. This was, of course, a situation neither of us desired as children, and it caused us both to deal with a great amount of adjustment as adults.