There's perfectly nothing wrong with you - at least, not on the
basis of what you've just typed.
The fact of the matter is you need to know who are strangers,
acquaintances and friends - blindly befriending any average joe or
plain janes doesn't exactly make them friends. This is especially
true if you happen to have friends who congregate in groups (ie.you
know and interact with them on a group basis rather than on an
individual basis). As most people behaving that way tend to make
friends on the basis of wanting to "fit in" to allay their
insecurities rather than befriending others through a common
interest/circumstance, such relationships normally wouldn't
withstand the test of time. In truth, such people will be spending
their lifetimes making friends in phases (ie.at school, work, etc)
without keeping any substantial friends that actually last a
lifetime. In all honesty, do you really need such friends?
Loneliness isn't a worthy reason to feed your insecurities methinks
- instead of viewing yourself as an outcast, you should feel sorry
for your insecure "friends" who seem to have numerous friends on
the surface, but are ultimately the loneliest people around.
Quality of friendships certainly far supercedes the quantity of
friendships.
If it's loneliness you wish to address, do go and join some
activities to interact with others as some have suggested. However,
don't bank on such channels as viable avenues for you to make
lifelong friends because, chances are, such "friends" (well, most
by the law of averages) will become strangers in the distant future
anyway.