Basically in the book the H cheats on the h and this is all due to him thinking she ignored him anyhow (not enough attention - poor child), they didn't love each other and he had fallen in love with someone else...now they had been married for twelve years, not to mention they were friends and of course when the h happens to look like she is moving on - bam! he wants her back!!
I mean would any self-respecting woman take back a husband who had cheated on her? Especially as this guy was her close FRIEND before they married (they had basically grown up together and he is unfaithful to her...), friends talk - dont they? shouldn't he have had the guts to talk to her, before he slept with the other woman? then he sleeps with her as well as his 'mistress'? Not to mention he expects her to still be friends with him and not be hurt! There is nothing redeeming about this H, he comes across as gutless and cruel.
He's broken her trust once, what's to say he won't do it again? By the time you get to the end of the book you hate his guts so the 'I really loved you all along' just doesn't work..