Not sure how he diminished her efforts at work. If anything he put her on a pedestal too high and suffered the consequences.
Pages 14-15, by claiming that his feat of surpassing her 7 years of effort in 6 months was a mere coincidence and not effort on his part. That was the first blow to her confidence and pride as an employee, as it can be taken as an accusation of laziness if it was that easy to surpass her.
Page 18, when she was having a vulnerable moment at work, he jabbed her once more by saying he's still inferior to her while showing off how far ahead he is in terms of knowledge and skill.
After all those attacks to her confidence, it was only natural she'd break down when the other guy, who was in a similar situation, offered a shoulder to cry on.
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emMeBi86:
But first of all he was deminishing his own success, saying that it was a coincidence while it was thanks to his efforts. She should have said that and "woken him up"
In a normal situation, yes. But remember that she was shocked by what he said so she meekly went with his request.