There's a book about this very thing: https://www.amazon.com/dp/B000UODXP0/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1
TL;DR: You seek novelty (ie chemical reward in your brain) in other areas of life, recognizing that long-term love provides other benefits.
A book that may help: Esther Perel - Mating in Captivity https://www.amazon.com/dp/B000UODXP0/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1