JD's coming back to Fandom this semester. Life ate my brain, I tried to eat life. One of us won.
So, his being absent for the last MONTH probably begs the question. Where has the bugger been all this time? The answer to this question is home. JD has been home. Meeting his "new dad". Given that his mother, cannonically, has married... often... it's not unreasonable to assume that she has remarried while JD is in school.
So, this is what happened. And the new guy decided he should get in good with the youngest son, and brought him home from school for bonding time.
After about a month, New Dad just couldn't take JD any longer, so instead of starting school back at home, JD (and Laddie) has been sent back to Fandom to finish out his highschool education.