First loves can be weirdly intense. It's a once only deal. But usually people understand the context and see it as no bad thing.
Very much this!
And, in this sense, I guess I'll also never love someone quite like my first love ever again. I was head over heels, and so was he. It was incredibly intense and emotional and therefore utterly consuming. I still love him to some extent and presumably always will. And I know he feels the same about me. That doesn't even mean I won't love anyone else as much. Just not "like this".
But, and that's one big hell of a "but": that's not what a healthy adult relationship is. And it's also not only love for the other person (which may really also rather be infatuation, I guess) but, I suspect, very much also love of the intensity and the all-encompassing nature of the experience.
My first love is now a good friend. We both have children with other people (and he's married to the mother of his). We've had plenty of chances to get back together - and we haven't and wouldn't because we're both grown arse adults and know full well that we're not really compatible.
Having said that, I'm very much able to experience intense crushes even in my 30s. I'm perfectly aware that they will not last an entire LTR but also very much wouldn't consider ever dating someone again with whom I didn't have this in the beginning. (Tried once, it was 2 years of drama-free boredom, he's the only ex of mine I regard as a mistake even though it was one of the "better" relationships I've had objectively.)
But then, these are conversations you have with your partner if you're absolutely confident they can cope and will see it similarly. I just wouldn't otherwise. It makes people feel insecure and may hurt them if they misunderstand.