The description of hypersexuality in your link doesn’t match losing interest in a partner as soon as there is familiarity. If anything, hypersexuality leads to wanting more sexual activity than their partner. That can contribute to fidelity issues, but that’s not the same as losing interest as soon as they get together.

ADHD doesn’t mean you can only be interested in novel things. People with ADHD tend to be impulsive and have trouble controlling how much attention they can allocate to each subject. They can still hold particular interests for years and decades.

The only argument for the behavior in the OC being attributable to ADHD, is that maybe they are compulsively jumping into relationships before finding out if they have any compatibility with the other person. So it’s not that ADHD made them lose interest immediately, it’s that they acted on impulse and started a relationship prematurely only to find out that they never liked the other person for more than their appearance. But that’s too much extrapolation for what is actually written.