From a purely Socionics perspective --

In a ESTp-INFp duality, it is for the ESTp to provide the initiative (as the extrovert) and "take charge" (as the ) and have the certainty of things (as the ). The INFp is to respond, and have the perception of how far to go and of the possible consequences ( ) and of the emotional state of the relationship ( ).

What I think may be happening is that the external circumstances work against that kind of duality. My guess is that the INFp doesn't really know what he wants and is sort of passive and indecisive; in more neutral circumstances it would be up to the ESTp to take charge. I suspect it sort of happened already, when you actually got together. But in the context of the military, and as he's the guy, a work colleague, and of superior rank, you can't really act as the ESTp "would" and be more assertive.

His not replying to mails can be the general passivity/indecisiveness, or just a concern about saying anything of that nature to a private over e-mail.

Again, I suspect he probably doesn't know what he wants or what to do of even if he's supposed to do anything.