My ex and I share custody of our 13 year old. I am moving 3 hrs away and my son will stay with his dad for school. what is a fair custody arrangement?

I have dealt with this situation as a Baltimore, MD child custody attorney.  A typical arrangement will be something along the lines of (a) the ex has custody during school months, while you have custody during the summer, (b) during school months you have custody during the extended school breaks for certain holidays, while (c) still alternating the actual holidays themselves, and (d) you would have designated times to communicate with the child by skype or Facetime, along with reasonable text messaging, email, etc.  You and the ex may also agree to more visitation (i.e., during the school year you would still get at least one weekend a month while the ex would get at least one weekend a month during the summer). Ultimately, whatever is fair and proper depends on what you and the ex agree is adequate for the child's development and familial bond.  Feel free to contact my firm if you would like an attorney to review or prepare the agreement, or file Maryland modification of child custody papers to make it formal.