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It may be worth going to court for depending on the calculations. I am curious if this parenting time is court ordered? If so, she cannot legally withhold for failure to pay. If not, he may want to establish court ordered parenting time in order to avoid the constant worry. Your fiancee may be able to combine parenting time and child support motions into one court hearing. Feel free to call for a free consult and I can discuss this more with you 952-237-8946
This is a tip-toe dance that many men who were never married to their child's mother experience. From what you describe, it sounds as if he has not established paternity or has an court-ordered parenting time. If this is the case, the mother can (and often does) dictate the terms of dad's time with his child and dad has no grounds to object. Men are often reluctant to discuss the issue of child support modification for (reasonable and well founded) fear that upsetting mom means not seeing his child.
It's worth sitting down with a family lawyer such as me to discuss what options are available to him and what is reasonable to expect to be paying under the current child support laws. Hennepin County also has wonderful court services that are good at helping people settle parenting time disputes.