One of the hardest things at times to do is honor others relationships. Life is weird in that if we show disrespect for others' relationships by trying to court another person away from their partner, then we open ourselves to the exact same situation against us in the future. In other words, if you try and take a girl away from her guy, the time may come when some other guy tries to do the same to your girl. If/when that happens, you will have no reason to complain as it was a tactic that you also employed.
If she leaves him for you, could you trust her to never do the same to you? Would you respect her more if she demonstrates that loyalty and fidelity are so important to her that she must politely deny your interest? One of the hardest lessons for men to learn is that sometimes a woman is friendly just because she is a friendly person and feels comfortable in a platonic way to other men, even while they are in a romantic relationship. Its called being a healthy balanced person. I made the mistake often when I was younger of assuming just because a girl smiled at me, chatted with me, had much in common and sought out conversation with me, that it meant she liked me more than just friends. Yes, at times she did, not the great majority of the time, she just saw me as a friend. I embarrassed myself many times asking these women out.
Boy my surprise when they were suddenly made uncomfortable by my suggestion to go out!
When you asked about the guy, she openly told you it was her BF and that they live together after 2.5 years. That is a relationship that is going in the direction of greater commitment and sharing of daily domestic life. Time will tell, but for your own sense of integrity, please consider keeping it platonic for now. If its meant to be, it must happen organically between you, not by telling her of your attraction for her. Now that she has told you of her romantic status, to ignore that and tell her of your interest anyway will look to her like you are barging into her life and disrespecting her intimate life.
Given all that, there are things you can do to find out if she digs you or not. if she asks you again why you have been absent on text or FB, simply tell her you were dealing with romantic issues that preoccupied your time. If she asks what they were, tell her that you had previously met someone that you felt fond about but found out that she was in a relationship. Tell her is was a disappointment but life moves on. See what she says. If she counsels you through it, she is definitely your work buddy/contact/friend. If she doesn't even ask more and politely does not inquire further, she is definitely showing respect for your privacy or she might suspect that it is her that you were referring to. If so, sense her reply and subsequent interaction with you.
Remember, if you just tell her your feelings, it may freak her out and she and you have to interact unavoidably in a work situation. Dont make your work life suck too. Also keep in mind this fact:
lets say you tell her your feelings. Lets say she is flattered and keeps the dialog open with you and time passes, getting to know each other more and more. If she decides to go deeper with you, it will mean she will break up with a man. It will mean great turmoils for both of them. She will really really look deeply at you to see if all that is worth it. She will want to know who you really are. It will mean that she will have to pack, move out, find an apt and move in. This takes day or weeks and takes an emotional toll. Remember you havent met her in person yet. You think you know her. But being in the flesh is another type of knowing in relationships.
At this moment in her life she is happy. She has a man, a relationship and has friends including you. If in time, her relationship sours, if she finds they can not live together and decides to move out, then you can tell her your feelings as you would have shown yourself to be a person who respected her life and relationship. that is something she probably can find attractive and admirable.
For now, I would use this time to quietly observe her and get to know her. In time, you will see even more about her that will help you determine if she should stay a work acquaintance, friend or romantic interest. I hope this helps you see it from a different perspective.
PJL