How do I commit to a partner?

This question primarily targets happy longterm couples.

I feel like my (23) generation is bombarded with an endless feed of pontential partners. It’s a constant “Hey you, you could do better than your current partner with his few shortcomings. Somebody else could suit you much better.” But being happy with your partner 24/7 just isn’t reality. And altough I understand this concept intellectually, the nagging of there could be someone much better doesn’t go away. I feel guilty and sad about these thoughts.

When there is just nothing wrong with your partner, chemistry is there, they have amazing communication skills and you just have a longing for more. For a constant dopamine rush instead of a steady, loving, sometimes exciting, sometimes boring relationship.

Also reading through multiple Reddit posts on the common relationship subreddits, every interaction is called a “red flag, dump him”. What’s that nonsense?
So, as I myself don’t have many positive relationship examples I went on r/happyrelationships to gain some confidence and hope in my relationship.

Please happy, loving, long-term folks, give me some insight on this! Have you questioned your partner? Why? How do you make your relationship work years after?

Tl;dr how do you commit to a partner? Have you ever questioned your partner choice?