Yeah I've seen this a hundred times, both in myself and others - a guy gets a girl all hot and bothered, then he does something stupid and messes up the courtship, and the next guy that approaches her gets a free ticket to her vagina, no matter how unsuited they are as a couple or how much lower value he is than the first guy. Usually he is lower value, since women are constantly staving off the unwanted attention of lesser men, but the next one that comes along gets straight in, and she had previously been single for months or even a year or so.
I don’t mean to make women sound so fickle at all - there’s a lot going on, but that is the sequence of events. If I could take a stab at explaining the psychology of it in simple terms; she feels like the exciting push-pull romance is the thing to blame, eg. she was just being played, and the next AFC that comes along and tries really hard, she finds it safe and comforting, decides he’s what she really wants right now, and goes for it.
HellHound has some really good info, but he's a bit careless about the fact that this is a work-place romance, and there is the potential to get into big trouble and put your job at risk. It's why people say never to get involved with your house mates because if things go bad, you won't just lose them, you'll lose your place and have to find somewhere else to rent. (That never stopped me though... hahah...)
The stuff he says would be true, but you don't want there to be material to file a complaint against you.
As for the other guy - I find it odd that someone you happened to confide in just so happens to be her boyfriend. It could actually be a coincidence, but on the other hand I have heard guys tell other people that he is her “lover” or some creative term when the girl is spending time around him but won’t commit. Perhaps there are more guys around the office like him?
Anyway - continue on as you have previously, whatever has worked. She hasn’t spoken of him, even when she could have used him as an excuse when she told you she was busy, she didn’t - so whatever reason she feels she doesn’t want to dive right into you yet, he is even below that.
You gave more information in the email to me than you did here, and while I won’t break the confidence if you don’t want me to paste it here, I found your choice of actions strange.
What I think is going on is you’re not really in tune with being the best “you” you can be. You over-think her actions and make bad decisions based on that. There are times when you’ve gone all out and been too AFC, got a bad reaction, so instead you pull right back, and completely ignore her in key moments. That’s classic PUA mentality. “Oh, giving her attention turned out badly, so I’ll give less and less attention, that will make me cooler and cooler”. No - the guy that gets the girl is super positive and engaging, and yes he has his own schedule to keep but he is never rude, and he can always detect an expression of interest, and MOST IMPORTANTLY - give it the respect it deserves.
For example, typical PUA mentality results in this; a girl finally asks a guy out on a date, or asks for sex, or even hints at wanting to hang out, and instead of “rewarding” the IOI, he acts all busy still - which she will rightfully take as a blow off - and suddenly she goes cold and distant and he wonders why she never talks to him again. One thing that classic PUA training teaches which is of great value, is “punish bad behaviour, reward good behaviour”. But a lot of the advice pushes the “bad guy” or “indifferent cool guy” mentality too far, and guys end up ignoring girls in key moments.
You could try a happy medium of HellHound’s advice - try and do what he said but don’t do anything that could get a complaint filed against you - by her or someone who was watching. A slap in the face, while it might have the result HellHound described, in the office will be a thing that will be filed as a complaint, and what will actually happen is the complaint will kill the romance - she may start to feel all hot and bothered, but when she finds out you’re being punished for it, it will tell her that yes it was indeed a bad thing you did and she will feel duped again.
Don’t over-think what she’s doing - girls don’t work in the logical realm so much in social interactions, the way we may try to. You will go crazy trying to work out what her motivations are by every single text and glance etc. etc. and you will end up in entirely the wrong place, because you should be looking at the emotional side of the interaction. For example, saying she’s got lots of plans could really mean that she feels she needs to demonstrate higher value because she’s feeling insecure. The bottom line is, women will display a wide fluxuation of behaviour both in the words they say and the actions they do, and none of it is indicating a certain outcome. Men’s role in a relationship is to be the certainty. Irrespective of how she behaves, you keep being the best man you can be, and yes you still pay attention to her behaviour in the moment, eg. she may be angry so you may have to placate her, or she may be ready to chat so you could further the conversation.
I have been in this situation before - that is, things were going really well, then I messed it up, and now things are in this strange place where she hates you but still tries to talk to you... like giving you a chance. Try to remember there is still that chemistry - so she’s not playing mind games with YOU, she’s just acting on the fact that you rejected her and made her feel bad but she finds she still has feelings for you. So naturally this is going to show a wild fluxuation in behaviour. So what do you do? Don’t take on her bullshit. Yes it’s your fault she’s behaving crazy, but this is still the best course of action - just steam-roll through being the best guy you can be, She will most likely take issue with something you did, and it won’t even make sense - eg. complain you are staying near her when you’re just passing by, or comment on the inefficiency of the way you’re doing something when you actually have very good reasons for it, or you absently slipped up but it’s just a minor thing and not worth the fuss she’s making about it. What you must NOT do is respond with an attack. Don’t get upset, and don’t berate her for her stupid logic. What you MUST do, is, when that happens, and ONLY when that happens, not afterwards, is address her directly, and calmly and plainly state your case, be assertive about it, be heard, but don’t be confrontational - and then continue about your way as if it never happened.
It’s hard not to react emotionally but you must train yourself to respond calmly yet solidly, and not aggressive in the slightest. Feel free to rehearse possible situations and outcomes in your head - it will help give you some where to direct the energy of the turmoil inside you, and it will also actually help you plan and form sentences for if that thing or something like it, happens. If you find your theoretical responses going negatively, start again and take a different tact.
Otherwise, keep being the guy that attracted her. If you find an opportunity to make her a present again, something that you KNOW will be good, just do it and don’t be afraid of the consequences, and show that you’re not afraid. You’re just doing a good turn which may be appreciated or rejected. You are still comfortable with yourself either way.
Notice I never mentioned the "certainty" being getting with her at all. You being the "certainty" is being certain about yourself, and being comfortable with the fact that things may or may not work out. If she has to move overseas, that's an example of it not working out, it has nothing to do with you, and it never should. You are just old and wise enough to know that's life, and you're always aiming to be the best you can be and gaining knowledge and experience in the process.