I think the beginning of something is so exciting.
It's the time when you might know all the other person's nicknames, but not their last name. When you know exactly how much taller (or shorter) than you they are, but don't yet know their shoe size. You know the sound of their laugh but not whether or not they snore. You are familiar with the size of their hand in relation to yours and if they prefer to hold hands with the fingers interlaced or wrapped, but you don't know yet if they are right or left-handed.
You know that the longer you know this person, the secrets and mysteries will eventually dry up and if they do snore it probably won't be as cute as it might be right now. If you stick together long enough you'll eventually know all the sizes and shapes and sounds and preferences.
This is the moment when anything could happen. You might end up not even liking this person much, or maybe you will for just a short time. But whether it burns out tomorrow or lasts sixty years, today you don't know. Today is butterflies and hope, excitement and desire.