Go ahead and steal her. It's a dog-eat-dog-world. Just make sure you have the muscles and the martial arts skills to fight the other dude when he comes to beat the **** out of you.
Remember, if you weren't stealing other guys' girlfriends, then they'd be stealing them from you.
However, BECAUSE this is a workplace scenario, you might wanna just **** the whole thing. Women act on instincts, and change their emotions in a heartbeat. Maybe she puts out Monday, and maybe she hates you Tuesday. In the workplace there are SERIOUS sexual harassment laws that you shouldn't break, and if you **** this **** up, and the girl who "likes" you today decides she doesn't like you tomorrow, you will get an asskicking from the boyfriend, and also get called a stalker at work by this girl, which could potentially lead to a sexual harassment charge and you losing your job.
Don't **** where you eat, aka don't try to bone co-workers. Even the roughest, toughest PUAs I know advise against this.