Pessimism, detachment

I've always had high standards for relationships, maybe unrealistic standards. I met someone 5 years ago who seemed perfect and we've been dating every since, for almost 5 years. Nothing has changed in real life, I feel like I have almost nothing to complain about but I feel the relationship fading anyway. Maybe relationships that start too intense don't last? Or my mindset isn't good for long term stability?

Do all relationships fade? I never believed people when they said all relationships do. I thought they were settling. But in spite of having such high standards I'm now... Disappointed. I've also been told that children who didn't see their parents show affection for each other have a harder time maintaining long term partners.

Am I just overthinking it? How do you know if you should move on or if you're self sabotaging yourself?

And if all relationships do fade, what would be the point of starting over?

I'm starting to doubt my own feelings, like I shouldn't be able to feel so detached from my partner for no reason, like he deserves better.

Any insight is appreciated.

Anyway I hope everyone is having a good day.