There are two things at works here. First of all, this guy isn't as serious about you as you think. If he can fall for another girl so easily and telling you explicitely that he wants to go out an experience with other girls, it means he's not ready to commit to anyone.
Secondly, you completely confused him with your insecurities. If you knew what you wanted when he tells you how you feel, instead of changing your mind a few days later, then he wouldn't have to guess what your feelings are. Your allowed to be confused about what you want, but it makes him really insecure being around you. Cause in his mind, he has no idea when you're going to change your mind again.
Sounds like he's ready to move on with other girls, otherwise he wouldn't risk getting close to another girl and even telling you about it too. I suggest you forget him, avoid contact if necessary to get over him. Here are the no contact rules:
http://www.askmehelpdesk.com/relatio...qs-332732.html
It's going to be extra tough if he's your co-worker (if i read correctly). However, if you keep talking to him while he talks to other girls, it will just prolong your pain and suffering.
Moreover, in the future, make sure you know what you want before you get so close to someone. Otherwise you're just leading them on and the worst part is, YOU end up being the one who gets hurt.