Collins Dictionary definition:

If you say, ‘out of sight, out of mind,’ you mean that people quickly forget someone if he or she disappears.

e.g., The problems of the poor are primarily invisible–out of sight, out of mind.

My boyfriend and I broke up when he went to work in Australia—it was a case of out of sight, out of mind.

Translation to Brazilian Portuguese:

‘O que os olhos não vêem, o coração não sente.’

‘Longe dos olhos, longe do coração.’