He's married but he has a girlfriend on the side.

他有妻室，但暗地里还有一个女友。

《牛津词典》

Otherwise, their child could end up one of those sad, pale creatures who can't make eye contact and has a girlfriend who lives only in the virtual world.

否则，他们的孩子可能会成为那种无法进行眼神交流的、悲伤苍白的生物，还有一个只生活在虚拟世界里的女朋友。

youdao

He has a girlfriend.

他有一位女朋友。

youdao

I wonder if he has a girlfriend.

我在想他是不是有女朋友。

I want to 实战 - SpeakingMax英语口语达人

And you also have classes that will give you an insight into, someone is coming to see you, who has an alcohol problem, a drug abuse problem, things you will engage in daily activities, boyfriend girlfriend problems, having trouble in class.

和其他课程，比如,有一个人来找你咨询，他有酗酒或者是吸毒问题，或者其他会在日常生活中遇到的问题，男友女友的问题，课堂上的问题等等。

普林斯顿公开课 - 人性课程节选

For those of you who are on the run from the FBI, your Visa has run out, or you're sitting next to your ex-girlfriend, now would be a good time to put a paper bag over your head.

被FBI通缉的,签证失效的,还有前女友就坐在旁边的,赶快找个纸袋子把脸给蒙上

耶鲁公开课 - 博弈论课程节选

"I hate the term 'bachelor pad, ' " says Mr. Davis, who currently has a girlfriend.

WSJ: Looking Out for No. 1 - WSJ Mansion

Dating seemed to be out of the question when he was heavier, but he now has a girlfriend.

CNN: Weight losers combat fear of exercise, schoolyard torment

"A few of the women in the building flirt with me on Saturday nights when they come home drunk, " said Mr. Rodriguez, who was quick to note he has a girlfriend and two kids.

WSJ: Finding Beauty at the Door