Girl at work likes me but has a boyfriend?

So I work with a girl, who has been dating her current boyfriend for about 4 months, we have been working together for about 2 months. There is no doubt about it that we both have feelings for each other and are attracted to each other, when we are out at lunch people have actually came up to us and said we are a cute couple etc... She always tells me how unhappy she is with her boyfriend and that she would much rather hang out with me than him, its a very odd strange situation. We have hung out a few times outside of work and had a blast, we always have a great time together and we have amazing chemistry, but somethings gotta give. Recently I have told her that you know I think its best that we just be work friends and stop hanging out after work (going to lunch everyday) and all that does is cause her to get upset. I really have no clue what else to do, I am a good judge of character and there is no doubt that she likes me more than her boyfriend but I was thinking its time to give an ultimatum any advice?
Girl at work likes me but has a boyfriend?
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