The relationship between Catherine and Warrick is very professional, and it is clearly emotional in the romantic aspect.
Season 5 Edit
A great demonstration on how they have a crush on each other is explicit on "Down the Drain", when Catherine falls into Warrick's arms and they stare at each other in a somewhat romantic way.
Season 6 Edit
When David Phillips tells the team that the victim died in no longer than 4 hours, Catherine sarcasticly comments that 4 hours is no longer that Warrick's time as married.
Back at the lab, he tries to explain her about it, and she says that this situation made her feel uncomfortable, says that she'd like to meet his wife, but suddently changes subject, thus showing that she felt jealousy or dismayed.