Oof. Do you REALLY want to know what's going on? Because this sounds like exactly like something I would do.

1. You've experienced the "INTJ Stare" - google it. It's not personal. If we look at the world while we're calm and emotionless, we know the data we take is accurate and trustworthy.
2. The fact that you still have contact = he's interested in you and wants to know more.
3. "Nothing in return" = he's VERY SLOWLY revealing who he is on the inside, with trepidation, in case you decide to bail at some point. This minimizes the pain for him later if you do.
   
4. "Once I agreed to go out it's like all that stopped" = He feels he caught you and the pursuit is over for him. Now he's trying to figure out what to do next.
5. His "NT" is trying on dozens possible futures where you're a couple, a little like your NT is. He hasn't settled on one yet because he doesn't know you well enough to filter through them all. However, especially being "I", talking about being a couple this early in the relationship is perceived as creepy, so of course he's not sharing the possibilities.

I know this has a weird vibe. It's really not. Think about it. You're trying to figure him out, just like he's trying to figure you out. But with INTJ, you don't know that he can already see being with you for a long time. He likes you! Why not entertain that? He doesn't want his heart broken if he commits too soon, and he doesn't want to show you that he's already putty in your hands.

Give him some time to process and give him more info about what you like and don't like - start superficial, and be brave to discuss deeper opinions and preferences quickly. Believe me, he'll integrate it all, begin to talk more, ask more questions, offer some of those possibilities, etc.

Best of luck.