Concisely explained.
Infatuation deals with huge amount of feelings and emotions without having considering practical aspects in a relationship.
A time frame of scene which there are two person/a pair of lovers dwelling in their own lovey-dovey world.
Love sets it's vision way further then the former.
It probably disregard most of the disadvantages in a r/s and overlooks most flaws of another partner.
It's somewhat similiar to infuatation....however the implications and meaning of LOVE should not be associated with infatuation or crushes. Though many times...relationship starts of with emotional rush and roller coasters rides.
During infatuation, every act are forms of love, but without eternal implications. Words and actions are all just out of excitement or rush of emotions.
My statement is subjective...so i'll just end here.

Love bears greater depth (That's why you seldom don't see man saying lovey dovey things to women/ or they don't commit)
Hmm....to your question why can't infatuation last.
I would refer to Uncle agony(You know who you are

) or Mr jOhO
Basically i don't think i could live in this world just by feelings...