Sex, of course, is mostly tension. Have you thought about this? Your dick gets hard and your pussy wet, when your sympathetic nervous system activates, when you react to something, when tension builds.
It is the contrast between that, and the activation of the parasympathetic system in orgasm, that makes it all feel so good. The more tension, the more powerful the potential release, by contrast. Maybe this is why some people like being tied up.
What is the contrast? What if you are completely relaxed? Do you need sex? I would say yes, but would the feeling not be different? Would it not be more frontal cortex based, more relationship based, more connection based? Something without a firm line moving in, where pleasurable feelings can happen without sexual arousal, and end pleasurably without orgasm, say in dancing?
If we posit that addiction exists to release tension, the amplitude of that release also needs to be factored into the rewards of addiction.
How, to put it another way, can I swim into and out of pleasure, all day every day? This is logically the opposite of addiction.
I think this is a very good question.
Edit: I will add that thrill seeking is not about fear, but about fear and release. It’s sex of a sort.