Aquarius is an Air Sign. That means they are thinkers. They like to be mental. Also, with Uranus as their ruler, they hate living by other's rules and need to be independent. Emotions aren't logical to them, so it's hard for them to really think about emotions and translate that to a word or action. Plus, emotions can sometimes be seen as weak by other people and the Aquarians know this. They don't want to be weak, in fear of being manipulated into following someone else's agenda. They have their own agenda and are quite passionate about these agendas (usually saving the world, being a humanitarian, and being everyone's best friend). This is not to say that Aquarians don't have emotions. They have emotions like everyone else does. They just don't show them and don't super know how to show them. They'd rather come up with a logical solution, and when an Aquarian does open up to you emotionally, be touched but don't expect anything. They'll probably run away from you afterwards. They don't like being vulnerable like that.
Also, what sign are you? If you're a Water or even a Fire Sign, I could see how this may bother you more than others. Just be patient with Aquarius. They have their moments, once they trust you and see you as someone they can mentally bond with.