It is all too common
In Melissa Orlov’s book, The ADHD effect on Marriage, she describes this very thing.
In the beginning, the partner with ADHD “Hyperfocuses” on the person they are with. The person is swept off their feet with all the attention. After a few years, or after marriage the hyperfocus wanes, because things are not as new and exciting for the ADHD partner. and the “Non” partner feels unloved or ignored when the ADHD partner is focused on other things like video games, TV, Porn…etc.
This has not happened like this in my relationship with my fiance. We have been together 4 years now.