#!/bin/bash
s="abc ঐ fdd"
sed -E 's/((ঐ|||ও|ঔ|ক|খ|গ|ঘ|ঙ|চ|ছ|জ|ঝ){1,3})[[:space:]]*/\1\n/g' <<< "$s"
IyEvYmluL2Jhc2gKcz0iYWJjIOCmkOCmkeCmkiBmZGQiCnNlZCAtRSAncy8oKOCmkHzgppF84KaSfOCmk3zgppR84KaVfOCmlnzgppd84KaYfOCmmXzgppp84KabfOCmnHzgpp0pezEsM30pW1s6c3BhY2U6XV0qL1wxXG4vZycgPDw8ICIkcyIK