I like this guy that I work with. We're friends, but we flirt a lot and he seems to make it obvious that he's into me. We're always touching and asking about each other's lives and taking breaks together and staring at each other. The problem: He's had a girlfriend for 3 years. We've only known each other since last April. His friend had brought his girlfriend up with him as a casual conversation topic, and the guy that I like hesitantly said, "I've been thinking about breaking it off with her, but I'd like to do it after her birthday which is in a couple days." That was about a month ago. As far as I know they're still together, and it's very confusing and frustrating to me. We talk quite often, and even some of my other coworkers have been telling me that he seems very interested in me. I've been questioning whether he's a player or not and if he's just leading me on. But considering how long he's been dating this girl, I'm doubtful. I wouldn't ever consider being with him while he's still in his relationship since I have been cheated on before and I know the drama and pain that comes afterwards. I don't want that to happen to anyone else, especially involving me. I would just like to know what to do in this situation... or just simply have an idea of what might be going through his head?

You answered your own question: you are doubtful, and that's all you need to keep him at arm's length. Add in the fact that this is a work 'relationship,' then that's double the reason to stay away!
One person often ends up losing their job when things go wrong!
Ordinarily it's OK to let someone know you like them more than a little, but not when that person is entrenched in a long term relationship.
If you think he's the type who has to be totally in a new one before letting go of the old one, then he's not worth getting involved with. He'll just do that to you someday, and it shows he's selfish - it's not fair to HER.

If you want to find men who are actually available, then tell him that you need to stop all this artificial fun. On the other hand, if it's fun and you can avoid falling for him, then let it continue.

You guys must be pretty young if you are confused about what's going on, and what to do about it. Assuming you asked him if he had a girlfriend before you started spending so much time at work together, then you would have backed way off then. If you didn't you should have. To even allow a guy who is committed to get so close is allowing him to cheat, and you already know the dishonesty and drama behind that, and you can bet he isn't telling her about you, anymore than he told you about her.

That you allow this at work is worse, since more drama will surely follow if he does dump his girl for you. How old are you both? Did you for fact ask him if he had a girlfriend when you started taking those breaks together? I doubt it, because then you would know he may not be a player, but he is willing to find another girl before he ends it with the one he has.

You have already let this go to far, and need to back up, and cut this workplace relationship OFF, before it gets really messy at the place that pays the rent. At best he is a guy who can jump from female to female, and at worse he doesn't mind going behind his girlfriends back. How is he not cheating on her with YOU?

The biggest thing you should ask yourself is why you don't know if they are still together or not, while you keep staying close at work. This drama could have been avoided altogether had YOU asked the right questions from the beginning of this whole thing, like the first time you took a break together!

Yeah sounds like you both are VERY young. Under 20 for sure, but teens is my guess. Am I right? Are you sure he is interested in you, or just wants another girlfriend? Would you get a new boyfriend before you dumped the old one? Is it any better being cheated on, or cheating with a cheater?

Await your thoughts on these questions.