Connection - Why does it happen and how do you continue to keeping it spicy?

The word is whichever you prefer to call it, Connection/Chemistry/Comfort. Why is it that sometimes we connect with some people and can relate to them as if we have known them forever even though we are meeting them for the very first time? Why is it that with some people we are able to let our guards down with ease, while with others we tend to be pleasing and politically correct so to speak. Why is it that with some people we only feel the friendship vibe, where as with some we feel the "let's just do it" vibe and with some we completely loose our minds and all of our senses, as in 'both of the former'? Why is it that with some people we can "appreciate" their beauty but might not necessarily desire any kind of relationship with them? Whereas with some people we feel so 'connected with' that love happens or grows over time. Do you believe in destiny, Soulmate, and/or coincidences? Do you believe that there is someone out there in this world for everyone and there has to be thousands of situations or circumstances that rearranges itself for two people to come together? Did you meet your partner when you were "ready", or are you a serial monogamous and cannot be single; or are you someone who is an "interpersonal perfectionist" who has a list of all the characteristics that you desire in a partner but are yet single, unless all the items on that list are checked off? Under what circumstances did you meet your partner? How did you know that your connection with them was so intense that you knew that they were one. Do you believe in love at first sight; Or did your love for them grow overtime. Did you look at your partner the first time and know he/she were the one and were left speechless or did your connection develop with your partner due to your attraction with other characteristics that they brought to the table.  Did you think your partner was "the one" or were you settling because it seemed like the right thing to do at the time. For my readers who believe in the institution of marraige, does the concept of 'connection/chemistry/comfort' even take any precedence over your choices of being with that person possibly for eternity or did the 'time' factor take precedence? Through my expericiences, dialogues and research over time I find that relationships that tend to be intimate, healthy and exciting revisit the concept of connection periodically. By that I mean intimate relationships just like other things in life tend to get stagnant or boring over time, especially after children, and for them to stay exciting and Ooo La La'ish' its important that your connection with each other is revisited. 
Relationships are about 'two' people and in our lifetime we as people tend to CHANGE! If the ideas that you started out with, are the same ideas, values and fundamentals you operate your relationship with today, the chances are your relationship is stagnant; and there is nothing too exciting like the kind of excitement that you felt when you first connected when you were in the honeymoon phase of your relationship. I have been fortunate to be surrounded by couples whose relationships are very sound, 'connected' and intense as if they fell in love yesterday even after being together for more than 10 years. A friend of mine who is currently in one of those relationships' once corrected me by saying, that kind of experience happens when you are 'growing' in love and not falling in love! It's about the mentality you carry towards your relationship, do you wish for it to be healthy and successful and are working towards it everyday; or are you letting life take over?
So then you may wonder what does 'revisiting' connection/chemistry mean? I believe it involves number of factors such as nurturing each other, being creative and surprising each other, sex - how often do you have it and what efforts do you make to switch it up, simplest acts of kindness towards each other, not forgetting to still impressing each other like you did when you first laid eyes on your partner and let love happen! How often do you do date nights and how spicy or steamy is your relationship?