There is an obvious difference between the sex you have with someone new and the sex you have with someone you've been with for a while. This can even be with the same person. To me, as a polyamorous individual, I believe that this is something I want to keep experiencing. I want it all. I want to experience the rush of sex with new people, and I want to experience the comforting sex I've had with someone I've had sex with many times before.
So let's look at 'new sex'. Think about the first time you're with someone new. Think about all of the wonderful anticipation and nervousness as you begin to explore each other for the first few times. The first time you undress in front of someone is a powerful experience. It all feels as exciting as things in middle or high school were. Suddenly you're placed back into that adolescent level of anxiety. It's a truly beautiful thing. You explore this other person in the most intimate way you possibly can. You hold your breath and the feeling of their hands on your skin is amplified a million times. You eagerly anticipate their every move, their every touch and caress. You become impatient. You want them to hurry up and end your agony of wanting all of them. You can tell a lot about someone in these first moments you spend together in an intimate way. Do they try to caress you? Please you? Tease you? Do they go straight for the gold? How do they touch you? New sex is one of the most exciting, powerful things one can experience, in my honest (drunken) opinion. This is what we would call the 'lust' of sex.
Now, familiar sex is on the other end of the spectrul. You may not feel that same rush each time you undress that person as you did the first person, but it's all still just as satisfying. It's on a completely different level. You've been there already, and you know you'll still be there for a while. There's really something amazing about the comfort you can find in being completely naked and comforable with someone you've been intimate with countless times. You know the ins and outs of each other's bodies. You know what drives the other person nuts. You're more inspired to be creative and to try new things, and this is a wonderful challenge. You know just how to push that other person's buttons. It's much more emotionally attached. Sometimes, you can skip all the foreplay and other nonsense, and get right down to business because you're that comfortable with each other. Familar sex is much more solid, much more stable, and much more comforting. This is the 'love' of sex.
Both types of sex truly have their place in live. Imagine sex as a house. When you first move into it, you map out the floorplan. You make plans for it. You enjoy putting your personal touch on everything. You unpack everything and it suddenly becomes familiar after a while. Then, after some time, you have a history there. You have memories. You know the floorplan so well that you could navigate it in the dark, and you feel much more comfortable there.