I think the key point you need to know is that most of the political parties in Singapore, and all the left-wing ones in Malaysia before independence and even after, wanted a unified country, and many in Malaysia even sought for a “Pan-Indonesianism” which would fit into the historical cultural realm of the Malay archipelago (the spoken lingua franca of the entire region prior to European influence).
I know nothing about this subject. Is it sort of like what happened with Hong Kong and/or Macau?
Somewhat.
I think the key point you need to know is that most of the political parties in Singapore, and all the left-wing ones in Malaysia before independence and even after, wanted a unified country, and many in Malaysia even sought for a “Pan-Indonesianism” which would fit into the historical cultural realm of the Malay archipelago (the spoken lingua franca of the entire region prior to European influence).