not reciprocated or returned in kind
"Moreover, a good solution for unrequited love is, of course, new love." Lucinda Rosenfeld, Slate.com, Nov 16 2010
About the word:
Where there's unrequited, there's requited. So what does requite mean? To requite (a somewhat quaint term) is to give or do something in return for something that another person has given or done.
So 'unrequited love' suggests an imbalance: too much love paid out and too little paid back.