yeah, thats cheating. Your telling the person you are available and willing so either you are which means you are cheating (and going to cheat sexually) or you are not and you are leading him on either way its a really shitty thing to do. Stop thinking about yourself and start thinking about how your actions affect others. Obviously you don't really deserve your boyfriend if your willing to put yourself and him in this kind of situation.
It depends on how much you fancy them and your intentions. If you are hoping or willing for things to go further than that then yes, it is wrong. End it with your boyfriend because obviously you aren't 100% happy with him.
It sounds like a fantastic idea. Honestly, it might be a little disrespectful toward the guy you fancy, going out for drinks if you don't want anything to happen with him, just don't lead him on and make him think he's getting somewhere. You'd be safe letting him know you fancy him, but are in a relationship... just maybe not over drinks.
What's your intentions with this person? How does your SO feel about it? I wouldn't do it but if there's no harm in it then make sure your SO if fully aware of the events and everything so there's no room for jealousy