Remus still thinks about James; how could he not? There are reminders everywhere - from the little, like his Quidditch team being mentioned on the radio, to the large, in the form of his look-a-like son.
He thinks about him on his birthday, just seventeen days after his own, and imagines what he'd look like now. He thinks about him every Halloween, the anniversary of his death. He thinks about him in random, every day moments, and realises over again just how much he misses him.
(He misses Sirius, too, but then he knew Sirius as an adult.)
Mostly, when Remus thinks about James, he thinks about how unfair it is. Because Remus is happy, happily married, with a child, a son: all the things James should have been. James' third grandchild was born last year, a baby girl, and when Remus holds her in his arms he thinks about how wonderful a grandfather James would have been, should be: how delighted he would be, how proud.
It hurts, because who would ever have thought that Remus Lupin would go far, and James Potter would die barely out of his teens? James, who did it all properly, who loved his wife and son so, so much, who would never have deserted them for any reason …
Remus knows how lucky he is. He leads a charmed life: a beautiful, clever, dangerous wife, a wonderful son – even a job, thanks to the new order of wizarding society built by Harry, Ron and Hermione. He is surrounded by love and joy and peace, and he is able to look back on the past without feeling much pain, especially when he does it with Harry. The two of them spend hours together with Remus talking, telling stories about James and Sirius and Lily, and Harry listens eagerly, hears about the past he never knew. A few years previously, shortly before the birth of Harry's first son, they went looking for information about Harry's other family, using Remus' knowledge. Harry now knows who his grandparents were; he even has photographs. While it's nothing compared to what Teddy has – two actual living, loving grandparents in the form of Andromeda and Ted – it's a lot to Harry, and Remus knows it might not have been possible had he not been alive.
But it feels wrong, in some ways, that he should have survived to live with Harry's generation – see Harry get married, have children, become the finest Head of the Auror Department the Ministry has ever seen – when James did not. Remus suspects that when Harry looks at his godson, he sees a boy who had the childhood he did not, a boy who could have been an orphan, could have lost his parents in a war, but is instead happy and healthy and loved. When Remus looks at Teddy, he sometimes sees himself as he could have been had his life not been blighted by lycanthropy, but other times he sees what James should have seen in Harry. The first steps, the first Quidditch match, the first wand. He is so lucky.
On September 1st, Remus sees his son off to Hogwarts for the first time. Teddy waves from the window of the scarlet steam engine, waves to his mother, father, grandparents, godfather and all his other doting relations who come to see him off, his young face alight with excitement, ready to go off to that magical place and learn and laugh and find friends, friends as good and as loyal as Sirius and James.
Remus never expected to return to Platform 9¾ after he left at eighteen. When he left again, at thirty-four, he knew for certain that he would never return. Now, at forty-nine, he knows he will return time and time again to see off and to pick up his son; then perhaps again, for Harry's children. He just wishes that James had been able to experience it all: putting his son on the train, armed with the Marauders Map and dozens of other tools for mischief, feeling proud and happy and sad all at the same time, feeling the love that comes from seeing your child follow in your footsteps, knowing you survived to see it.
Remus smiles and waves one last time, missing his son already and missing his friend, too.
About Ted - I wanted Teddy to have at least one set of grandparents, so this is what happened: Ted was on the run, but not killed; Remus, Tonks and Andromeda didn't know if he was alive or dead, thus Teddy was named, just in case. And then after Voldemort went bye-bye, Ted returned to his family and was naturally delighted to find a grandson named after him. :)