How do you stop being insecure?

I've been talking to someone and its my first time on the dating scene in almost a decade (29 years old, yeah I know), when I last dated someone, there wasn't all this talk of situationships, "talking stages", poly/open relationships, or at least it didn't feel like that.

Now this person I'm talking to, they have told me they're going on a second date with someone, and despite them telling me that they enjoy the time we spend together, its hard for me to shake the feeling that I haven't been good enough, hence them dating other people. And, to add salt to the wound, my own attempts at going on dates with other people hasn't been succesful.

So I guess my question is, how do I stop being insecure? How do I hold myself confidently while accepting that a relationship may not successful. How do I grow from this?

Ive asked plenty of stupid questions on this sub before, but any insight would be appreciated.