if 劈腿 means 愛情上有第三者或是濫交, 一般常聽的英文(美式)說法為:
1. he/she is seeing someone(another one).
2. he/she is cheating.
3. he/she likes to fool around.
4. he/she is a player.
5. he/she is flirty.
6. he is a dog.
7. 也有人說 he is a stud(情聖)
另外 unfaithful, two-timing, traitor 和
double-crossing等等也都有人用過.
"have the third person" 的說法實在相去甚遠,也非一般英文用法. 首先have動詞有擁有的意思,你不太可能去擁有一個人. 所以有第三者的動詞不適合用have. 再來, third person一般來說應該是具有不明確的身分,也就是說應該為某一個人. third person is more like someone rather than a certain one. 當泛指某一個人時,用the當其定冠詞是不恰當的. 應該用 a. 除非thrid person(party)已經特別被定義過了.