What's wrong with being happy?

I was watching "The Real World: Austin" tonight--my first mistake, I know--and was really annoyed with Danny, who was having a hard time accepting the possibility that he had actually found the right person for him in Mel. The pressure from other roommates to sleep with other women compounded his dilemma. Danny seemed convinced that there was something wrong with being with just one person who made him happy instead of a seeking a string of physically gratifying but ultimately shallow short-term relationships. The confusing part was, Mel satisfies him physically and he admits that "it's not about the girls," and yet he was still compelled to sleep around.

While Danny is an extreme example of, what roommate Rachel called, "the curse of the penis" (I'm paraphrasing), I still think that his problem is more widespread than many people might think. Many women seem unsatisfied in good relationships, too. Why is that? Why are people so afraid to just BE HAPPY?! Admittedly, my relationship with Mandy got fairly serious fairly quickly. However, as we near our 3 year anniversary on October 15 (I got her present today, I RULE), I've never once regretted our time together, despite common assumptions/expectations about how folks should act in college, or wondered what I was missing out on. I'm happy, I'm completely satisfied, and I'll just never understand why someone in a position like mine would ever want to fuck with that.