用英文表达“不应该出轨”可以有多种方式，以下是一些常见的表达方法：
- It is not appropriate to cheat on one’s partner.
- Cheating on your partner is not acceptable.
- One should not engage in infidelity.
- It is wrong to have an affair with someone who is not your partner.
- It’s not right to betray your significant other by having an affair.
- Infidelity is not a recommended behavior in a relationship.
- Cheating is something that should be avoided in a committed relationship.
- Having an affair is morally wrong and should be discouraged.
- It is important to stay faithful to your partner and not to stray.
- Unfaithfulness is a breach of trust that should not be condoned.
这些表达方式可以根据具体语境和语气进行选择和调整。