Have boyfriend, but am very interested in a co-worker...?

I've been with my boyfriend/son's father for 4 years. For the past 3 and 1/2 years, he has been abusive and disrespectful in every way imaginable. Needless to say, I've pretty much lost any love I had for him. I'm planning on leaving him after Christmas (don't want to upset his family who we've been living with for a while). I really like my co-worker that I've known for several years. I was trying to keep him out of my head, because I still felt like it was wrong while still with (Jerk). Then, I brought up a subject last night having to do with fantasies and my boyfriend admitted he thinks about his female co-workers ually. He talks about the girls at work quite a bit too. Am I allowed to plan on asking the guy out when I'm single and is it OK if I flirt a little for now? Cheating in my book is a big NO in any situation, so I don't plan on that. Any advice!!?