"The one you love and the one who loves you are never, ever the same person." Invisible Monsters, by Chuck Palahniuk
My initial thought: How much do our perspectives (not necessarily truth or reality) play into how we see a loved one and them us? Cause I've met people who I've wondered how their better half deals with them...and have thought the same for my poor husband at times!
And then take into account a number of things, such as maturity level, experience, situations, needs, wants, etc., that can arise between two people, for good or bad. There's something to this I think.