... so its just a lot of observations on each others part. i wonder if he's a sensor, because he seems to be picking up on things quickly that my ISTJ friend is really good at - if im feeling quiet or acting a certain way, she notices this immediately, whereas my N friends don't really seem to get this. they just intuitively know im not feeling well but they internalize it immediately so they dont need to ask or study me to know it.
I don't know exactly your history with him, but if you can find a reason may be you can just approach him a few times for some simple task/request/question. He'll start thinking about it. Then may be make a counter move. If he is taken ... well then he should stop staring at you

... but may be he is single or doesn't like his current gf that much, who knows. At least this way you'll send a bit of a harmless signal to him.
... this is why i think he is estj - I read that ESTJs and INFJs are dualities in socionics. I read in socionics that it's difficult to notice your dual partners at first and easy to pass them by.
Greencoyote and I have been trying to make sense of socionics and basically in some material INFJ is INFj and in some INFJ is INFp. Socionics apparently had different branches and the authors of these branches were developing them separately and were not in agreement about terminology and function assignments. Doesn't help that it was all translated from Russian so the translators might not have known about this disagreement in russian psychology community. And different websites seem to reference different material sometimes mis-matching INFJ profiles on INFP functions.
So I switched to using
Wikisocion like Greencoyote is doing and by that system INFJ is INFp and so our duality partner is actually ESTP. ESTJs is predicted as conflicting partner. Apparently weakest point (point of least resistance in socionics) in INFJs is Te, it is way weaker than our Se. It is like our super-blindspot. Their Te is primary and we cannot clearly see it or effectively respond to it. Our Ni hits them in similar manner because it is their point of least resistance. What it amounts to is a lot of not seeing things same way at all. Conflicting partners don't actually have to conflict, they can be coldly polite, and this is what I feel is going on between us. I've noticed that emails that I send he translates sometimes in completely foreign to me way and then there is potential of conflict there. I say one thing - he understands another thing - then I cannot understand how he arrived there. ENTJ is supervisory relationship where ENTJ acts like a teacher and tries to each Te to the INFJ. Both relations are classed as repulsive.
ESTPs I have been dismissing also, but I've known 3 and we by far understood each other better than this ESTJ I came in contact with. Once you learn to get over all of the stories of all the girls they had sex with in past, it is actually not that bad lol. I've also recently found myself attracted to an ESFP guy, supposed to be semi-duals. I can say we are indeed sort of protective of each other's Ni and Se. According to this website INFJ-ESTP pairs are actually pretty common, as are ESTJ-INFP pairings:
Compatibility and Your Myers Briggs Personality Type | PersonalityDesk
... but he might be an xSTP as well.