How to make a move on a girl at work?

Long story short been working with this chick for 4 months. Eye contact and flirtation is there. she has a boyfriend but she constantly complains that she isnt satisfied and wants to break it off. I recently got her number and suggested me, her, and one other colleague all hand out one evening for games and drinks. Should I have invited her out just by herself?
(these are my opinions i am not a licensed broker by trade)