In my language there is a word to describe what I feel: SAUDADE. This word only exists in portuguese.
Saudade was once described as "the love that remains" after someone is gone. Saudade is the recollection of feelings, experiences, places, or events that once brought excitement, pleasure, well-being, which now triggers the senses and makes one live again. It can be described as an emptiness, like someone (e.g., one's children, parents, sibling, grandparents, friends, pets) or something (e.g., places, things one used to do in childhood, or other activities performed in the past) that should be there in a particular moment is missing, and the individual feels this absence. It brings sad and happy feelings altogether, sadness for missing and happiness for having experienced the feeling.