I vaguely remember the word that I was encountered earlier that can be roughly summed up as the Title. Not entirely sure if it's a word or a phrase. It's been bugging me for a really long time, i need help!
Do you mean someone who lives vicariously?
vicarious- Experienced in the imagination through the feelings or actions of another person. Acting or done for another
Perhaps not exactly what you're looking for, but useful nonetheless:
Compersion -- 1. The feeling of joy one has experiencing another's joy, such as in witnessing a toddler's joy and feeling joy in response. 2. The feeling of joy associated with seeing a loved one love another; contrasted with jealousy.
It's often described as the opposite of jealousy and is common among parents and the polyamorous.