Epistolary problems why part two of Uncertain Glory doesn't work

Part one of Joan sales' novel Uncertain Glory (1971) ends w the protagonist, Lluis, meeting w his morose and cynical childhood/college friend as both are away from the front in Barcelona during the Spanish civil war; the friend - Julio? - chides L about a number of shortcomings and at last reveals that he has been carrying on a relationship w L's partner - Trini - they are committed to each other and have a child of about 6 tho neither believes in marriage - for some time. This revelation/confession of course startles L but as a committed radical he has no ground on which to stand and of course he has during much of the past year been pursuing a beautiful widowed woman (without success). We don't yet know anything about the relationship between j and T except that they have been in correspondence throughout the war. Part two - each part of this novel is about 150 pp - consists of trini's letters to j, which j give some to l and which we now begin to read. We see right away that l unlike j has been an irregular correspondent and that the letters (and occasional visits bearing cartons of tinned milk ) are a vital part of t's life during the years of war and separation. Frankly though Trina's letters to J are a bore - long accounts explaining why she is a committed Christian despite her radical politics, an account of her baptism in a clandestine service - all members of the clergy were at risk of assassination by radical groups - and a long account of her sheltering one of l's relatives, in mortal danger as a factory owner. Theough the civilian life during the war seems like a potentially great topic w so many killings and acts of terror T's letters - perhaps intentionally - are so matter of fact and bloodless as to undermine and deflate the narrative. Additionally they're not credible as letters even in the days of epistolatory novels - far too long to believe anyone but a novelist could or would have composed them.