Was my brother's guilt justifiable?

His wife had a hard time conceiving their first child for nearly 3 years. She finally naturally gave birth at the age of 34. Their daughter is now 4 years old. Her egg count was much lower than usual for her age; between ages 23-26 were her good years.

He felt guilty for making her wait too much when they were boyfriend and girlfriend, for taking her for granted at the time. He proposed shortly after she broke up, she forgave him, accepted his proposal and they got married the following month. He was willing to pay for her whole fertility treatment. He didn't want her to help him with the bill. At the time, he kept telling me ''This is my fault. I'll never forgive myself if she can't get pregnant''.

Was his guilt at the time justifiable or was he being too hard on himself? From time to time, he still feels some guilt that they can't another child nor two more. He blames himself.

Updates
3 mo
His own words he recently told me ''If I could just turn back the clock, I wouldn't have wasted her time, I regret it. We would've probably had 3 kids by now''.
Was my brother's guilt justifiable?
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