i really like what mmhmm said... for the sake of relationships, i think of "love" as like long-term, and infatuation as short-term. but i also don't necessarily believe in "the one", or that the ideal relationship lasts a lifetime.
anyway, for me, i get VERY infatuated too -- spend much of my time thinking of them, about them, etc. i think about how well we work together, the color of their eyes, etc. and i tend to be infatuated for long periods of time. years. and it's hard for me to get truly annoyed at them, or if i do, i think it's me that's done wrong. and i do love them, as in care very deeply about them, but it hasn't crossed that threshold of no return.
so then there's a certain point when i realize, i could be with this person for the rest of the foreseeable future - and that's ok with me. that conclusion is a HUGE deal to me, because i'm veryyy P, and i do not not not like making decisions and closing doors. because choosing that one person means NOT-choosing the other 6,854,750,033 people in the world. and when it's ok to permanently reject 6,854,750,033 options... that's pretty much it for me.
i think there's a lot to be said about shared experiences, too. love grows with seeing someone in so many different situations and understanding them and watching them learn and change and struggle and triumph. that can't really happen with infatuation.