Love Signs: How To Know For Certain If Someone Is In Love?

I know that I love someone whenever I think about someone a lot like in this part of the lyrics of the love song that the sapphic artist called Chloe Moriondo wrote dedicated to her girlfriend named Samantha at https://youtu.be/Aaz3zN3FLFU?si=NZxoGWJoqcPGIULa :

And everything I write sounds cliche, but

I can't help that I think about you every day

And every night

And every morning

And afternoon

And all the time...

How else do you surely know that you are in love?