They would have been painful reminders

[keannu]

He, an immigrant with the mother tongue of Spanish, regrets that he is in an uncomfortable situation of not being able use old calling terms for his parents. What does the underlined mean? It seems to mean "If I had used mama and papa, they(mama and papa) would have reminded me of how much had changed in my life."
but what change did he mean? I'm sorry this might be something you have to infer from the context, but it might be a piece of cake for native speakers.

ex)My mother! My father! After English became my primary language, I no longer knew what words to use in addressing my parents. The old Spanish words(those tender accents of sound) I had earlier used- mama' and papa' - I couldn't use any more. They would have been painful reminders of how much had changed in my life. On the other hand, the words I heard neighborhood kids call their parents seemed equally unsatisfactory. "Mother" and "father", "ma", "papa", "pa", "dad", "pop"- all these I felt were unsuitable terms of address for my parents....

st-100.2

[keannu]

I think it's probably because of many changes in the foreign environment. He has to experience different people, different houses, different music, whatever new culture you encounter, etc, so using "mama" and "papa" would have made him miss the past memories back in his home country to escape from the current situation. If you have any different opinion, please let me know.

[SoothingDave]

The "change" was that he had assimilated to an English culture. He was unsure whether to continue to address his parents using the terms (in Spanish) that he used as a child. They reminded him of the life and culture he had left behind.