Some questions about the veracity of The Sense of an Ending

Moving onto the second half of Julian Barnes's "The Sense an Ending," the confusion deepens: first half or so set this up as a 60ish divorcee (Tony) gets a letter for a lawyer and learns that the mother (whom he barely knew) of his college girlfriend (Veronica) has bequeathed him 500 pounds and the diary of one of his prep-school friends (Adrian) who'd killed himself (wrists, bathtub). Veronica, now holding the diary, declines to give it to Tony. They meet in London and she hands him instead a copy of a letter - a really cruel letter he'd written to her and Adrian back in their youth (she took up w/ Adrian after she and Tony and split). OK, first of all, there's no way in creation that Tony would have forgotten that he'd written this very cruel letter. Second, will we get any explanation at all as to why the mother had left Tony the $ and the diary? First half of Sense of an Ending was a little troublesome because, as noted in yesterday's post, it seems like an outline rather than a novel - rushing through plot elements and across time without sufficient detail (though there are detours for lots of meandering thought on the nature of history and how we can know the truth about past events - bright-student ruminations, but also a commentary on the nature of narrative fiction and the fallacy of memory in the absence of documentary evidence) - but now in the 2nd half, as Barnes slows the pace in order to let the plot develop some gravity, I'm not sure what the point of the plot is, after all. I remain curious, however, and will definitely get to "an ending" if not to "the sense."