The act of sex isn't necessarily primitive in itself, but merely a way man has adapted to produce offspring, one of the most basic of instincts.
Now, we have evolved to enjoy and be open about sex and our preferences. Probably through pressure, or whatever influences people have on others, we decide to experiment with partner(s) to get the most amount of pleasure.
Now, on the other parts:
1) Sex is overrated.
Not necessarily. Sex, as in the act, releases endorphins, which can lower stress levels. Now sexual/sensual content in movies, books, and the rest of the media IS overrated, simply because that constant stimulation eventually desensitizes us to the wonder and joy that is sex.
2)Will it become boring if you're with the same person over & over? (that's how I interpreted that point. correct me if I was wrong)
Again, not necessarily. For example; My husband and I have been together over a year now. True, we are a young couple, but we have also been through what can be called the 'make or break' of a newer relationship: a baby. Even when I was 8 months pregnant, had a 56" waistline, and weighed 190 lbs, we were still just as crazy about each other as we were when we met. Now that I've had my baby (see profile picture), and I'm about 50 lbs lighter, the sex is still incredible, that is, when we get the chance to. This leads me to my point: When two people are REALLY in love, sex doesn't get boring. The connection you get from such intimacy fuels the relationship. If you aren't in love, then things can get stale pretty easily.