I think yours is an identity crisis more than anything. Have you
ever wondered by whose standards are you measuring your "inferior"
self against? And on what basis do you conclude such yardsticks to
be the appropriate benchmarks to be measured against? Look, if you
were talking in pure academic terms, I suppose I could still
understand if you failed to measure up in terms of your grades(at
least, there's something tangible even though it might not be a
comprehensive and accurate reflection of one's ability), but how
you could find an 'acceptable standard' to measure your personality
and character is just beyond me. Taking your last point about
emotional detachment as an example, it's pretty obvious there isn't
a particular type of person who would fit into all sorts of social
setting - case in point : oftentimes, a talkative person is
unlikely to get on with a quiet one without the pair ever
regretting not getting to know the other party(quite simply, the
quiet one will probably view the loquacious chap as being too noisy
for his liking and likewise, the talkative chap viewing the quiet
bloke as too reserved for him). Hence, is there even a realistic
chance of having a 'perfect' conversationalist who could appeal to
both the quiet and the talkative chap? You just can't ever please
everyone in life, can you? 
First and foremost, I think you need to resolve that ambivalent
dilemma more than anything - what is it you really want and what
are the things which constitute being acceptable?
Personally, I don't see how this "Im likeable enough for most
friends to behave cordially towards me, but not enough for them to
include me in their social life" syndrome should ever affect
anyone. The reason being human relations and chemistry between
people work in such subtle ways I don't believe going out of your
way to fit into the culture of others is ever a solution to your
problem, even if it's fuelled by a deep sense of insecurity. I mean
if you had some common interests with those whose social circles
you're trying to be a part of, I can't see why they wouldn't want
you in them. That said, if you're not a part of their social
circles simply because you do not share their culture(which is most
probably the case anyway), then I don't see why you should feel
desperate(and dejected when you don't succeed) to be a part of the
group either. In truth, you're probably better off not being a part
of someone's life with which you cannot really identify with and
feel miserable being anything but yourself just to accomodate
him/her.
Don't read me the wrong way though because I'm not trying to
encourage you to be anti-social by any stretch of the imagination,
but I think it is imperative you understand(and this isn't rocket
science 
)
that it is not likely you'll find an intellectual in the company of
street thugs; a teetotaller in the company of alcoholics; or an
atheist in the company of preists. In essence, do mingle with
people if company is what you seek - however, do not feel
compelled(and deem yourself a failure in the process) to fit in
with a particular group if there is simply no chemistry between you
and those whose lives you wish to be a part of. I'm sure there're
enough people out there for you to find those who share your
interests, passion and values.
I suppose if you could resolve the ambivalence in you, points 2 and
3(ie.relationship and emotional detachment) will pretty much take
care of themselves. When that happens, I don't see how you could be
that bothered by your physique anyway given you'd probably feel
more confident and less inferior. 
As Bill
Clinton famously remarked, "Life is shaped by the opportunities you
turn down as well as by those you seize."
