I work with this guy and I really like him but he also has a girlfriend. We have a great time talking at work and I’d like it to be more, should I tell him?
No, you should not tell him at all. If he is in a relationship you need to respect that no matter how much it may suck for you. If all you two have going for you is that you have fun talking at work (and assuming his relationship is good..you didn’t say if he talks negatively about it), then you have no business trying to force a wedge between two people that are perfectly happy. If he was single, or if he eventually is, let him know how you feel. Until then, zip it.