I've pondered your questions for some time now. For me it boils down to logic. I know I would sincerely "give all", die, make great sacrifice for many. Logically, I am sure that many,many others must feel the same towards others as well.
Here enters the complication. The many disappointments we've all suffered, and sometimes been the source of, have taught us that those we most expect to "go to the wall" for us often don't. On the other hand, we are often surprised by the acts of kindness and altruism of those whom we are little aware of.
I can't believe that it's all a sham( the whole love thing), but I do think that we tend to, as a rule, misplace confidences and loyalties.
Nvr