The speaker is talking to you. Hey! Yeah, you! Listen up! Don't worry, though. He's being nice.
He tells you that having a coke with you is just tons of fun. It is so fun, in fact, that it makes taking a European vacation look like a trip to the dentist (no offense, all you aspiring dentists out there). Specifically, it's more fun that visiting cool, seaside cities in the Basque country (north Spain/south France), and even more fun than feeling queasy in a beautiful neighborhood in Barcelona, Spain. (We guess that it's such a great area that even getting sick must be a blast.)
So, why is enjoying a carbonated beverage in your company so great? Well, in part it's because you look like an improved version of Saint Sebastian, partly because the speaker loves you (awww), partly because you love yogurt (no, not frogurt), and partly because you share secret smiles with each other. In a nutshell, the speaker's feelings for you are best summed up by the Carpenters.
All this lovey-dovey sets the speaker to thinkin'. You guys are so in love that statues are like… weird to him. How can anything be that still and defined, the speaker wants to know, when it seems like you guys are floating "back and forth / between each other"? And when he goes to the portrait show, everything he sees just looks like, well, paint, and seems pointless, compared to looking at you. Swoon.
You know what? The speaker would rather admire you than all the portraits in the world. Welllll, except for maybe "The Polish Rider," (what do you think?), but only on occasion. The speaker's happy that you haven't seen this painting in person yet, because that means when you when you do see it for the first time, you can see it together. Also, you move more beautifully than any moving figures that have been painted (like the famous one in "Nude Descending a Staircase") or drawn, even by Leonardo or Michelangelo. Come to think of it, all those Impressionist painters (like Monet and Degas) really aren't that great, considering that they never got you to pose for them. And the sculptor Marino Marini is also overblown, because his famous sculptures of riders on horses focus more on the horse than the person.
To the speaker, all of these artists seem to have missed out on "some marvelous experience," but not this guy. He's knows a wonderful thing when it's happening to him, like having a coke with you. And that's why he's just told you about it. (Could anything be sweeter? Only this bucket of bathing baby sloths.)