Please listen when the others are telling you that YOU need to make this decision alone. Do not give one second of consideration to your husband's feelings about missing out on this child's life. You are the mother and the responsibility for raising her will be yours (even in 2018). The relationship between you and her will be the most important determinant of yours and her happiness for many years to come.
Having listened to Dr Harley discussing your case, I have the firm impression that the reason he advised that the decision should be yours and yours alone is because you were greatly wronged by the affair, and you should not consider doing anything that means you will need to live with that affair, in your face, for the years to come.
It's true that the child's features, and her eventual difficult behaviour (that all children go through), and the practical changes that she makes to your lifestyle will remind you of the affair, but I believe that Dr Harley was advising against having the child of your husband's affair in your marriage - full stop. I don't think he was saying that it would be hard on you because, as the mother, you will have the primary relationship with the child. I don't believe he was talking about your having to do the majority of the child-rearing, because that's what mothers do. He was talking about the injustice done to you by the affair, and the fact that "just compensation" is owed to you by your husband. "Just compensation" means that the affair is erased from your lives, and that your husband does all he can to protect you from the impact of that affair in the future (and from other future affairs, of course).
"Just compensation" means that the wrongs created by the affair are barred from being a part of your marriage, and that the affair is put behind you and never mentioned again. It means that your
happiness is the primary task in your marriage. It does not mean that your husband is punished because of what he did, but it means that he must protect you
. "Just compensation" creates a happy, fulfilling marriage for both of you, rather than making the unfaithful spouse suffer for the rest of his life.
According to Dr Harley, there is a price that a husband must pay, in order for his wife to recover from an affair, when he has had a child from that affair. If the marriage is to be successful and fulfilling for the wife that he betrayed so badly by creating a child from the affair, he must have nothing to do with that child, beyond proving court-mandated financial support. If the wife is to feel
restored to her rightful position as the only woman in his life, the child, in effect, needs to disappear, mentally - and that includes not seeing her and her mother once a year around town. She needs to not exist, for the couple.
She won't "not exist", of course, because the wife knows that she is out there, and could contact her husband when she's older - and also, because a portion of the family income must be put towards supporting her - but there is nothing that the couple can do about those things. What they can control, however, is having her in the marriage. A husband who wants to rebuild his marriage must be willing to compensate his wife by, in effect, cheerfully volunteering to have nothing to do with the child. He mustn't fret about her welfare, or show that he is sad about not being the father that he is to his other kids. To do those things is to put pressure on his wife, which she does not deserve. She deserves compensation, which means becoming the "first and only" in her husband's mind, and in his life.