IPA: /ˈlʌvˌsɪk.nəs/
KK: /ˈlʌvˌsɪk.nəs/
A state of being unhappy or anxious because of unrequited love or longing for someone.
After she left, he fell into a deep lovesickness that made it hard for him to focus on anything else.
Lovesickness is formed from "love" (from Old English "lufu", meaning deep affection or strong emotional attachment) and "sickness" (from Old English "sēoc", meaning ill or unwell). The term describes a state of emotional distress or illness caused by love or longing for someone.
Think of 'love' as a deep affection that can make someone feel 'ill' or 'unwell' — that's why lovesickness refers to the emotional pain of longing for someone.