I wanted to throw out a concept that I came across about 2 years ago that I think could really help people understand what's going on in their minds when they first start spending time with someone they fancy. It can even be applied to a new friend, although it's mostly supposed to be applied to a love interest.
Now, this term, limerence, is kind of hidden from the general populace because it's mostly only used in the polyamory community. However, what it describes and entails is exactly what most everyone, poly or not, goes through when they first start dating someone, or even if you just find a new friend that you "click" with, which is why you may want to suddenly spend an inordinate amount of time with that new friend. It's the whole butterflies in the stomach, obsessing over the person, "honeymoon", and making possibly irrational decisions phase of a relationship. You know that Ah-Ha moment you had finally coming to terms with autism? Well, this kind of provides that same sort of Ah-Ha in regards to some of the feelings and thoughts you might have when entering into a new relationship, friendship or otherwise.
Magazine and online articles abound regarding this subject without actually giving it a name. However, the poly community has spent quite a long time addressing this issue, because while it affects most everyone starting off in a new relationship, it really affects a poly relationship when a new love interest comes available, usually because the person who is smitten has to keep in mind that they have other obligations to attend to, and it's easy to forget and neglect those obligations when your head is in the clouds.
So, if you'd like more info about limerence, you can read the limerence wiki page, google the term to find other websites, or check out other open/poly relationship resources and books. Opening Up was how I first came across this term, but only a small section is dedicated to it. Doing a bit more research online, I found all kinds of sources