What do you think the best ways to provide affirmation are, without it coming off as insincere, trite, or manipulative?There is somewhere a personality type description of INTJ which states something like this: what others perceive as an INTJ's self-confidence LOOKS the same, but is in fact qualitatively very different from the general,all-encompassing, seemingly ever-present, even if often un-justified or baseless self-confidence that others types, (like ENTJs) always project: an INTJ's self-confidence is of a very specific nature, stemming from the detailed knowledge systems that we tend to built throughout our lives.
Our knowledge systems are NOT built around emotions, and we do not invest anywhere near as much effort in examining, understanding and learning to read and deal with emotions (ours or other peoples'). Instead, our knowledge systems will over time develop ever more intricate and expansive knowledge maps and probability grids of things that INTJs genuinely see as more interesting and important than emotions. Anything, from political systems, to maths, to business, to economics, to programming etc.
This means that when you engage an INTJ on a complex issue that is unrelated to his emotions towards himself/herself or people that matter to him, you are likely to observe a suprising self-confidence in how the issue is approached, debated with others, analysed, used as a basis for conslusions and then those conclusions are used as a basis for decisions, which lead to actions etc.
However, when it comes to personal emotional issues, or recognising and dealing with the emotions of people who matter to us, we INTJs do not have the support of a knowledge system, that massive armour of patterns, theories, case studies and scenarios with which we equip ourselves when we fight the battles we trained ourselves to fight. In the case of emotions, we really go in to battle naked. And we know we are naked (we know what we know, and we know what we don't know...and in these cases we know that we don't know enough to successfuly deal with emotions, or to deal with them, work with them as well as most people). This is why you see us so unsure, so waivering and so 'insecure' in emotional matters.
We are not playing a game. We are genuinely clueless about our true emotions and even more clueless (at best , ever-doubting) the emotions of others. And we do not doubt their genuineness so much as we doubt their permanence.
This brings me to your other point/question: do we need constant affirmation of the other side's emotion towards us? The answer is yes. We do not need it in the sense that an F would need it. An F would become depressed or upset at a lack of such affirmation and constant "giving" or moral support/initiative from the other side. An INTJ is highly unlikely to become upset, but will grow doubtful of whether the other's emotions are still there, still as strong. And in the presence of such doubts, the INTJ will begin to take the only step an INTJ takes to protect oneself from further stress, dissapointment and emotional (gasp!) turbulence: distance himself from the other side. In the INTJ's emotionally primitive mind, this distancing kills two birds with one stone: it builds an emotional buffer zone that will lessen the force of what seems like an probable emotional blow and at the same time the creation of distance serves as a test of the other side's intentions: if the other is still genuinely interested in the INTJ, he/she will seek to close the distance by taking some initiative towards this. If the initiative is strong enough to be noticed by the INTJ, the latter can let his guard down once again, re-assured for the time being that the emotions are still there. Until the cycle begins again.
Yes, you do have to always take the initiative and you have to be prepared to play the role of the giver, almost never the taker, of constant affirmation on this front.
This is not easy for your personality type, for it doesn't come naturally to ENTJs. In my opinion, the only personality type who finds pushing forward and CONSTANTLY seeking to close that distance as effortless and natural as the INTJ finds retreating in self-doubt and building that buffer zone, is the ESFP.
I hope this helped you build some understanding.