It all depends on what you prioritise OP. @5128gap hit the nail on the head when they said "Excitement always gives way to comfort and familiarity. Some people are happy with that trade off, others always need the buzz."
You're human with biological programming that hasn't caught up with the fact we're no longer monkeys. You're always going to get that buzz from new people, because that's how nature gets genes spread about. In the "limerant" phase when we're high on hormones, we do indeed, look at no-one else. But that's scientifically proven to last 2-3 years max. After that the hormones ebb and are replaced by "cosy" bonding ones. So asking your partner and/or relationship to act as an anti-attraction-to-others mechanism isn't fair. It's physically impossible.
Which is where we come to the trade-off. When I was with my ex, did I feel a buzz when others were attracted to me? Absolutely. However, when I considered the intimacy between myself and my partner, the times we'd cared for each other, made each other laugh, all the small things, etc, etc it really quashed any urge to pursue it. Yes, these feelings were "cosy" and not "passionate" but they made the buzz feel psoitively coarse in comparison. So I was never tempted to stray.
Alas, my ex felt different. The same things that stopped me straying, didn't hold the same value for her. So she pursued the buzz, blamed our relationship (not me - I was fine, more like you say "if our relationship was good, I wouldn't be feeling an attraction to anyone else, so the fact I am means its wanting") and I had to file for divorce.