A great start to My Golden Days, and then what happened?

Arnaud Desplechin's My Golden Days got off to a great start - but then what happened?! A great beginning as Paul Dedalus (yes, we catch the allusion), a middle-aged anthropologist (as we later learn) leaves a central Asian republic heading home for France (where he had not lived for many years) and says farewell to a woman who works in the embassy and w/ whom he's been in love, or at least having an affair. All OK until he's stopped in a French (I think) airport and told there's a problem w/ his passport. That leads to an interrogation - French officials think he's been a Soviet spy - and flashback to his youth in southern (?) France and an adventure in Russia (I won't give it away), and a great story seems to be building: Apparently there's another Stephan Dedalus elsewhere in the world, same name, dob, place of birth. Now the spoilers: After the matter is explained, and we think we're building toward a crisis, the pin gets pulled and we learn the other Paul has been dead for 3 years, so what's the point? Then Paul has other youth memories, in particular, of his first huge college crush - and for the next hour we are faced with the tedious, predictable, terribly familiar romance story: his pursuit of "unobtainable" girl, he wins her heart, he goes off to college, they write to each other (dutifully captured in voice-over, a device that Truffaud used well and more or less retired). Completely uninteresting stuff, made worse by the fact that there are interesting characters on the periophery whom Desplechins (had to look up his name) leaves unexamined: the odd mother who dies when Paul is 11, the brute of a father who for no apparent reason later in life turns out to be a kind and friendly dad, the younger brother who's drawn to guns and violence, the attractive sister who believes she's "laide" ie ugly - why can't we learn more about these people? Why start a really good story and let it spin away into thin air? I couldn't finish watching - just didn't care after 1+ hour. Rather be reading.