My suggestion to the two of you, is to not fight over your son - your situation is as such to where a 50/50 completely joint custody arangement would be IDEAL for everyone - mostly your son. There is no "primary", neither of you have more say than the other. It could be worked to where one week you have 4 days, she has 3, and the next week, or every 2nd week it switches.
You two are already one step ahead of most divorcing couples, with your different shifts you are comfortable with the changing of the guard when it comes to parental duty. This is not something the two of you have to come to blows over.
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