Well, she has a fiance and there is nothing in your post indicating that her relationship isn't going well. If it wasn't, you would have put that info in there. So even if you want to sow discontent between the two of them, there doesn't seem much hope for that.

She is probably somewhere in between just having a nice time talking to you and giving you a shot if she were single. But she isn't. Her not leaving her fiance is a choice she is making every day. Yet you tell her 'you Love her and wish to spend the rest of my life with her'. Even if that is true, and that is doubtful as you are just coworkers talking, you really want to fore her to either stop talking to you completely, treat you as if you don't exist, or break up with her fiance?

Say she has a single female friend you happen to meet and like. Why would she recommend you to her for having put all this responsibility on her? What did she do to have to take on this responsibility for your feelings? Just because she decided to have a nice chat with you?

Maybe this is just my way to prefer to deal with everything. But I prefer to carry as much of the responsibility, of the hurting, as possible and to lighten the burden of my romantic interest. Keep it light-hearted and fun for her. People who start to take a liking to you don't suddenly want to deal with 'I will love you for all my life'. Especially not if they are seeing someone else.