Having a sexual or romantic relationship with someone other than one's spouse or partner; an affair/extramarital relationship.
彼の浮気が発覚して、二人は別れることになった。
His affair was discovered, and the two of them ended up breaking up.
妻は夫の浮気を疑い、証拠を集め始めた。
The wife suspected her husband's affair and began gathering evidence.
浮気は信頼を壊す重大な裏切りだと感じる人が多い。
Many people feel that an affair is a serious betrayal that destroys trust.
Fickleness or inconstancy in affection or interests; being capricious or unfaithful in feelings (not necessarily sexual).
彼は浮気な性格で、次々に趣味や仕事を変える。
He has a fickle personality and keeps changing his hobbies and jobs.
あの人は人付き合いが浮気で、本気になりにくい。
That person is fickle in relationships and finds it hard to be committed.
気持ちがすぐに浮気すると、長続きする関係は築けない。
If your feelings change quickly, you can't build a lasting relationship.