i know this was directed at the ladies, but i think i know what it is....
women are mad self-conscious and insecure in themselves
they always feel like nobody will accept them for all their personal and physical flaws, like if you really knew the real them...all the ugly and all the truth...you'd run scared....
so when they come across that dude that knows all the ugly...yet he still don't mind being around her they stuck.....
that's their security.....
with a new dude.....there's always a fear or an uncertainty that he may discover something about her he can't cope with and dip....but with old dude....there's nothing he already don't know...so even if her gets on her damn nerves 100% of the time.....she's still more comfortable with him than someone who don't know as much about her