When he lost Mum and Dad, Al still had Severus, who was there to hold him and be there and share the brunt of the experience.
Ben didn't have Ronan, and that, to Al, was incredibly difficult to wrap his mind around: how did he manage? It was hard enough to lose a parent, but to lose them all alone.
He hoped that Ben had someone - anyone - who split his grief with him. Someone who hopefully made it better.
"Um," Al bit his lip. "Ben, if you don't mind writing to me, in person, or by owl, and if you ever need assistance - with the house or otherwise - or have an urge for a conversation - written form of it, mostly... Just let me know."
Someone must have been there to get Ben through this far... but it didn't hurt to make sure.