Firstly, I want to call you out on something you said - "I know I have brought this on myself." Yes, you made an adult decision to be intimate, and it must have been amazing to finally be with someone you'd had feelings for for a long time, but you've done nothing blameworthy. This is just part and parcel of life's journey - we do some things that later turn out to be things we don't look back at fondly but we do what we do with the knowledge and feelings we have at that point in time. We can't predict what will happen.
I totally agree with socialmoth when saying that you have this opportunity to see your colleague's behaviour at an early stage before you get hurt later on. In my late teens and early 20s I had crushes and it felt amazing to be with them when it worked out that way, but what i realised is that who I have a crush on is not often a good indication of who I am compatible with in a meaningful relationship. I sort of felt star struck with my crushes and lived in the moment but always acted terribly awkwardly with them in other social settings. It was only physical and the rest was cringeworthy. Often I realised they only wanted something physical. I exerted so much time and effort hoping they would change and want a relationship with me but with the benefit of hindsight I see now that I was never made to feel good about myself with those people - like me, you (and everyone!) are deserving of someone who likes you as a package.
I know - easier said than done. But I know from experience that holding out hope that things will change is often time wasted, when you could spend that time developing friendships and connections with other people more suited to you.
As for how you behave around this person at work, would an option be to ask for a quick chat and ask to clear the air and just say that it was fun and you are happy it happened but that maybe you both shouldn't do it again? It's tricky trying to work out how to act. Another option is to explore other dating options - I have found in the past that meeting someone new magically makes me lose feeling for the other person, and you might gradually find that you become less awkward with the person at work.