1: He will just say the Magical Words!
When he says he loves you without you asking him or putting him under any sort of pressure. This means he’s saying that because he really wants to show his true feelings to you.
2: Does he really mean it? You can Judge!
You know the guy inside out. You can judge whether he’s really serious and into it when he says that. He’d say it without wanting anything in return (like sex, etc.) and if the only reason behind his words is his deep rooted love for you, then his words have substance.
3: The way He says it
The way he says it, Yeah it can be a bit movie-ish and cliché, but if he holds your arms, looks you straight in the eye affectionately, shows that he cares about you and says those 3 words. It is real.
4: Wait for the kiss
He says he adores you right after you kiss each other, and that followed by pulling you more closely and you can listen the pounding of his heart coming ever so closer to you and then he caresses your hair and kisses you again.