I have always thought that when a woman is pregnant, that is the best time to introduce her to having another guy join them. This is because no condom is needed to prevent pregnancy. So my hope would be is that she gets so used to letting the other guy cum inside her without a condom at least once a week. That way she gets at least 36 loads of cum inside her from him and in her mind fucking him bare is just as natural as fucking her husband. Then after the pregnancy she does not think anything about it and keeps on letting him cum inside her now unprotected and fertile pussy.