Instead of books try a relationship counselor. Not just about this issue but to develop communication skills that will transcend to all your problems. Then you can learn to resolve problems without fighting. Fighting can be taught as a skill so that you don't feel that you are fighting over small things. I understand your insecurities about this girl especially with a new baby. He need to make allowances for your feelings about her. You can also try the Mars and Venus series to develop communication but he needs to show that he can be a part of a couple by resolving this. Find a professional before the relationship cannot recover. I don't think it is about this girl but more about learning how to compromise and acknowledge each other's feelings.
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