Fast five - dom and girl cop relationship ?

in fast five, the girl cop that works with hobb, elena, what is her realtionship with dom. when they first meet, he say he knows who she is and saves her. when they meet in her apartment, she says something about something being special to him and he said he ddnt think anyone understood how much but she did. what did she say and what did they mean by that. iknow at the end, they are together but what was their relationahip during an before that ?