I'm not very experienced but here's my advice. There probably is no recovering from this, but here's what I would do. Clearly you've been showing too much interest and that makes you look needy and desperate to women (i've been there too). The first thing you need to do is stop obsessing over her. Stop saying things to her that let her know how you feel about her.
That's seems to be the point of push/pull tactics. Keep her on her toes, keep her wondering about you. Teasing and messing with her to build attraction. Be a playful dick. It's okay to be a dick as long as she know's you're just kidding.
If you work with her why not let her see you talking to other girls. Let her see them talking to you. Have fun with them too, teasing and messing with them. Let her see that you have other girls calling you at work. Have your sister call you at work if you have to (she won't know it's your sister). Trip her jealousy switch. People seem to want what they can't have, not what comes easy. And you were being easy in the past, way too easy.
Reframe the situation. You are the prize not her. Don't put her on a pedestal, or she will start to look look down on you from it. If she puts her self on one, nock her off of it. It seems to me that when I'm more invested in someone than they are me, I don't get anywhere. Make sure that she's more invested than you are.
Don't be her girlfriend who she calls to for advice about what she should do about this guy. Refuse to play that role. I would say to her, "I think you should come over and make out with me, that will take your mind of him". I would say that not real serious like, but with a smile on my face. If she say okay -great. If not then it's her loss -and it's probably time to get off the phone as well because you want to look like you have other things going on, like you have a life. And because you're not going to be her girlfriend.
Sounds to me like you're not good at building attraction. That's an area I need to work on also. I do alright with push and pull and cocky funny (being a playful dick), but I just don't have much to talk about. Nothing interesting, because there's not a lot going on in my life. I think we need interesting things to talk about, stories, routines, little games -something. Something to show that we're fun and interesting. Something to set us apart from other guys.
One more thing I would do. This girls dropping hints that she might leave, and the reason is probably because you are making it too awkward and uncomfortable for her. You are trying too hard, and you are litterly going to run her away. Back off a bit. Stop obsessing and investing. She will see a difference in you. She will see you talking to other girls. She will see that you have a life outside of her.
Then the next time the two of you are alone look her in the eyes and sincerely apologies for your behavior. You weren't getting her anyways so why not try this. Tell her that you realize that you were being desperate and needy, and that you know girls don't like that shit. Tell her that being over weight all your life has really messed with your confidence (which is understandable). Tell her that you realize that you've been kind of obsessing over her and then promise her that you are going to stop all of that. Then say, "it's just that I find you really attractive and sometimes I just don't want to take my eyes off of you". Like a line out of romance novel. Surely that will touch her heart. Then say, "I know I messed up our chances of getting to know each other better, and that really sucks." (Don't say you messed up your chance of getting to know her better as that sounds like she's the prize, say -our chances) Then tell her how you wish you could have learned this lesson before you meet her because girls as attractive as her don't come along very often. This might be a good time to touch her. If you're both sitting down you could put your hand on top of hers for a second, look her in the eyes and say, "so anyways I'm sorry if I made you uncomfortable". Then get up and leave the room.
If you have any chance of recovering with this girl it will be because she sees a change in you. So change. You aren't saying the above to make her feel sorry for you, but to make her realize that you understand why she's become so uncomfortable around you to the point where she might leave. (Don't say anything about her leaving though as that might make all this look like a last desperate attempt to get her to stay). She will then realize that you get it, and that you understand the situation and that will make her more comfortable around you, might even keep her from leaving. But, none of this will do you any good if you don't change your ways.
I think this all sounds like sound advice, but then again, I'm a newbie so who knows. This is just what I would do.

-good luck.