My partner and I are celebrating our 10th next month. Before I met her, I went through a few years of wondering whether I'd ever meet anyone again, and if there was something wrong with me. Then I overcompensated the other way and became what I termed "militant single" - actually OPPOSED to having a relationship.
Based on my own experience, I echo what others have said above. Stop focusing so much on it. Society, the media, even our well-intentioned friends and families put pressure on us to be one half of a heterosexual "couple". Rise above it - enjoy your life, do the stuff you like doing, be confident in yourself - it can happen when you least expect it, which makes it nicer. And when it does, it STILL might not be the one - that happens and we all have to deal with it.
Re the female colleague, don't take this the wrong way but I'd just advise you to honestly examine your expectations and your interpretation of her actions - is there a chance she didn't lead you on, but that you were adapting her behaviour to fit in with your hopes of what might happen? As I say, please don't take offence at that as it's easily done - hell, I've done it myself. If however she simply was leading you on, then you're better off out of it. Forget it. Concentrate on living your life for yourself, not in the hope of some notional future relationship.