Ok. Time to clear the air on this once and for all...
**Steps on soapbox**
You said:
Once he had understood why he had to leave and why his jealousy of Troy's life outside their relationship made him fear being abandoned and led him to pre-empt that by himself abandoning Troy first, Miles could put all of that into a letter to Troy. To offer the explanation and the apology that Troy deserved and that Miles finally could no longer avoid giving to Troy when they encountered each other in Edinburgh.
Miles DID explain why he never contacted Troy:
By the time I had come to terms with her memory, too much time had passed. Erik told me you were in a relationship and had moved to the East Coast. I didn’t want to rock the boat, so to speak. I decided to let sleeping dogs lie.
MILES TOOK THE HIGH ROAD AND PUT HIS FEELINGS ASIDE TO LET TROY LIVE HIS LIFE WITH OWEN.
That is what's known as a sacrifice.
And he did it with Erik's knowledge. So should Troy hate his dad for keeping something potentially painful from him? I'm sure Erik believes that he was protecting Troy, and in a way, Miles too.
As far Miles resisting temptation... He is. He made it a point to let Troy know that Owen is invited to dinner too. How painful must that be for him to acknowledge to himself that he lost what could potentially be the love of his life and still include him in a dinner invitation?
**Steps off soapbox**