The quick and simple answer would be Love,
The word is here is joining.
As a couple is formed and develops over time, The joining of two lives start to become one,
Personality starts to shape and inside jokes become something special, Every slight glance into someones relationship is a personal joy to see what makes two lives meld together.
Being able to spend time with two people and learning who they are together as well as individuals brings me a passion for the love they share,
Capturing the smiles, hugs, touches, personalities, and even some of the crazy things they bring to the table, ( nerdy, travelers, sporty or even just loving to watch movies together )
Each couple is very different from the next, I just wish I had time to get to learn about every one around me,