We have a friendship because that's all I want from him.
If I wanted something more, the relationship would have naturally moved in that direction. It never has and, trust me, it never will.
I have an INTP friend, too, (God, what are the odds?) and the two of them are starkly different, in my opinion. They don't always get along. I've seen the two of them clash and it's not pretty, but I can tell they have decent respect for each other. Also, I get along better (and I have a closer friendship) with the INTP. He's very... considerate and he listens to me. The INTJ?, on the other hand, can't really be bothered with my "theories." I hate to put it in these terms, but I'm just waiting for whatever usefulness I am to the INTJ? to run out, really .
Anyway, I honestly don't think he's INTP.
The INTP I know has a sweetness about them that isn't nearly as developed in this INTJ?.