All Oliver has ever wanted is for his brother to be safe, he just didn't know how to do it. And all Orel has ever wanted was for Ollie to be happy. Waaay back in one of the earlier chapters, he tried to share his most precious thing: Finn, with Ollie.
I think Orel knows that Oliver needs to go, Orel doesn't need protecting, and if Oliver walks now, Orel will be just fine. It's Tarquin that needs Ollie. I do enjoy how the dynamic we expected at the start of the book is completely inverted by the end.