I know this isn't what you want to hear, but I think you need to just cut your losses and move on for now. To be honest, it sounds like she was just enjoying getting attention from you but had no intention to take things further. Lots of girls do this, especially in the 18 to 24 age range. As women get older, they mature, and tend to move away from this type of behavior. This also sounds like a toxic relationship that you two have with the constant arguing. You probably just lust after this girl and do not genuinely like her.
Find other girls, DEFINITELY work on your confidence/neediness issues, and forget about her. If you can, don't give her more attention that you need to (or preferably none at all). Talk to other girls in the office and let her see you, but don't pay attention to her. Maybe she will become interested, or you can try again in a few months, but leave her alone for now.
You say you're a fun guy so if possible date at least two to three other girls at once. It will definitely help you get over your neediness as you'll focus your attention between multiple people and not just one. Try online dating if you have trouble lineing up dates...there are lots of horny girls
If I wasn't clear before, let me spell it out: SHE WILL BREAK YOUR HEART AND RUIN YOU IF YOU KEEP PINEING OVER HER!
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