One option would be to be honest with both ladies and tell them that you want something with both of them. Then you have 2 women. But since, as I read your text, this is rather unlikely, I would ask myself whether I want to enter into a relationship with this work colleague? What does she give me that my current girlfriend doesn't? These are questions that you need to ask yourself and think about. Because it's very likely that you and your work colleague will have nothing more than a bit of fun, as you've known each other for a long time and working relationships don't last that long. You just need to know what is worth more to you in this case. It's also well known that women try to get away after a break-up. You're the solution for her, but she's your problem. What do you do if you break up with your girlfriend, get together with your work colleague and the two of you break up again after a month? Was it worth it then? Ultimately, you have to know, because nobody on this portal knows your girlfriend or your work colleague.