He may not be talkative because he is still trying to get used to you.
If you are in a relatively new relationship with him, he may require more time to gauge your personality and get more comfortable around you.
Some people can be relatively quiet when they are in the beginning stages of getting to know someone or a relationship.
They may fear that they will say the wrong thing if they say too much too soon.
Hence, they would rather spend some more time getting to know you or getting used to you before they decide that they can be more extemporaneous and open with their conversation.
A guy like this may not be entirely certain about what topics are safe to talk about.
He may not want to jeopardize the relationship in anyway by saying something that would turn you off.
This is a guy that may not have had too many relationships in the past or may simply be very cautious when he starts one.
He may even want you to lead by example.
He may want you to do most of the talking so that he can become acclimated to what you tend to talk about.
The more you talk about that topic, the more he becomes familiar with it.
He may even go off on his own to learn more about it.
As time goes on, he becomes more confident in the topics you tend to bring up because these topics are now predictable.
He now knows what would be safe to talk about in your presence.
At this point, he may become more talkative because he knows what kind of topics to bring up.
Another reason why this guy may not be talkative may actually be because he is not as into you as you may think or believe.
I know that you have the impression that he is, but he just may not be.
Perhaps you have read too much into his body language or what people have told you.
Perhaps your own desire to be with this guy has clouded the reality of your situation.
If he hasn’t asked you out on a proper date, he may not be as into you as you believe he is.
If he rarely initiates contact, he may not be as into you as you think he is.
If he never talks about you to his friends or colleagues, he may not be as into you as you think he is.
If he rarely makes himself available for conversations, he may not be into you at all.
You have to be honest with yourself with what the reality of your situation is and what you are hoping for.
Those two may be completely different.
Now, if you do believe that he is into you and have irrefutable proof of this, the best panacea for your situation may be to simply be patient with him and allow him to get used to you.
At that point, he just may become more talkative.