The noun 前男友 (qiánnányǒu) means "ex-boyfriend," referring to a former romantic male partner. The prefix 前 indicates "former" or "previous." The corresponding term for "ex-girlfriend" is 前女友.
她和前男友分手已经两年了。
Tā hé qián nányǒu fēnshǒu yǐjīng liǎng nián le.
She broke up with her ex-boyfriend two years ago.
在街上偶遇前男友,气氛有点尴尬。
Zài jiē shàng ǒuyù qián nányǒu, qìfēn yǒudiǎn gāngà.
Running into her ex-boyfriend on the street was a bit awkward.
她说再也不想提起前男友的事了。
Tā shuō zài yě bù xiǎng tíqǐ qián nányǒu de shì le.
She said she never wants to bring up her ex-boyfriend again.