If you're referring to the years while he was at Hogwarts, JK never stated specifically if he had a girlfriend, but from what toi read from the context, toi could assume that Pansy Parkinson was his "romantic interest". If you're referring to who he married, it is Astoria Greengrass. :)
Well I personally think that in his hogwarts life his girlfriend was Pansy Parkinson. Although Pansy was always smothering him he still loved her. I also think that he teased Hermione because he had feelings for her, so Draco probably loved Hermione plus than anything in the world but, unfortunately, she didn't l’amour him back. And eventually, Draco went and married Astoria Greengrass. Now Tom Felton (the person who portrays Draco Malfoy) has a real girlfriend too. Her name is Jade Olivia.
The correct question would be who is Draco's *boyfriend* and that would be Harry Potter the famous weirdo himself... I mean, JUST LOOK AT THIS PHOTO!!! Probably one of the best but who am I kidding? I have waaaayyyy too many pictures of them...