The problem here is that mom threw all of her time and energy into the new relationship and it came at the neglect of her child. If you are a single parent I suggest a good balance in dating. Spend time with your kids. Spend time with the person you are dating. If you are already married in a blended family, keep a fresh connection with each child. Ironically, this will make it easier for your kids to embrace their stepparent and stepsiblings because they are not competing with them for you.