1) Ache 1) Pining 
Lovesickness describes the informal syndrome of rejected or unrequited love or the absence of a loved one and covers physical as well as mental symptoms. It is not to be confused with the condition of being lovestruck. Although typically harmless it can for some personalities lead to serious physical or mental illness, sometimes even culminating i...
[n] - a pining for a loved one
noun a pining for a loved one