“出轨”在英语中常见的表达有：
释义：指在感情关系中背叛伴侣，与他人发生不正当关系。
例句：
He cheated on his wife with his colleague.（他和同事出轨了。）
She found out that her husband had been cheating on her for months.（她发现丈夫已经出轨好几个月了。）
释义：表示与他人发生秘密的、不正当的感情关系，通常指婚外情。
例句：
They were having an affair for years before anyone found out.（他们在被发现之前已经出轨好几年了。）
It's painful to discover that your partner is having an affair.（发现伴侣出轨是很痛苦的。）
释义：形容对伴侣不忠诚，通常指感情上的背叛。
例句：
He was unfaithful to his wife, which led to their divorce.（他对妻子不忠，导致了他们的离婚。）
She felt betrayed when she learned that he had been unfaithful.（当她得知他不忠时，感到被背叛了。）
释义：字面意思是“偏离、走失”，在感情中可引申为“出轨、变心”。
例句：
He strayed from his marriage and had a brief relationship with another woman.（他背叛了婚姻，和另一个女人有了一段短暂的关系。）
She worried that he might stray if he spent too much time away from home.（她担心如果他离家太久，可能会出轨。）
释义：指同时与两个人交往，对其中一人不忠。
例句：
I can't believe he's two-timing me!（我不敢相信他竟然脚踏两条船！）
She found out that he was two-timing her with her best friend.（她发现他背着她和她的闺蜜出轨了。）
释义：指不忠的行为或状态，通常用于正式或书面语境。
例句：
Infidelity can cause great pain and damage to a relationship.（出轨会给关系带来巨大的痛苦和伤害。）
She decided to end the marriage after discovering his infidelity.（发现他不忠后，她决定结束这段婚姻。）
日常口语：常用 cheat (on someone) 或 have an affair。
书面或正式表达：可用 be unfaithful 或 infidelity。
非正式或俚语：可用 two-time (someone)。
stray (from someone) 较为文学化，适合特定语境。
根据具体场景和表达习惯选择即可。