Random meetings

Why do we have this undeniable "I got caught feeling", when we meet a co worker or someone we know with their girlfriend, that girlfriend we didn't know about, but we also not that close to each other - so why would we care?
I often think about situations like that - what do they even mean?
Does it mean that we are attracted to each other?what is this uneasy feeling that gets attached to this out of blue situation?

Is there a chance that your mind has formed a defense shield against the possibility of unrequited love? so therefore you are not able to feel like you have a chance to ever fall in love.

There are many theories regarding relationships among and between human beings. 
When do i know that I'm a part of the statistics made for these theories?

Yet again, a question arises, would i be able to feel again? or have i lost it forever?
Strangely, after a few tiring weeks - i went outside and breathed in the air and enjoyed the sun rays, that was quite magical.
Why can't we always enjoy it? why are we busy inside replaying our mind games?