intps don't spend much time in a vulnerable state. they appreciate that you get where those spots are, but, for the most part, they prefer to deal with their situation with Ti and Ne.
they are also rarely physically expressive. they express their ideas and values in logical principles. their ethics are principled rather than personal. their bodies are less feely and their eyes are blaringly loud and steely. they don't look away and demure very much. they are aggressive readers and not so much expressers.
they watch what you do, they are very behind-the-scenes in how they interact. so they may look like they lack initiative but they are not enthusers and not in-charge like enfj types are. they will step in when a problem is not being solved and they have the solution. otherwise they will recede a bit.
they can become more consistent when they realize it is effecting the situation negatively, but they are N types who tend to drift along with their thoughts and need external structure for this sort of thing.
i would be careful asking the person to change too much and realize that you may find some of these needs elsewhere. keeping in mind that what your intp friend CAN offer you is valuable in its own right- great Ti, some Ne to reel you in and get you in the moment, and appreciation for your abilities at getting into people and being in touch with their feelings.