…And what caused them to think about you, hmmm? *shakes head* It’s nonsense, and if “Psychology Says” it’s true, “Psychology” is even more full of shit than usual.
At any rate, the correct contraction of it is needs an apostrophe: it’s.
“Whenever you think about someone a lot, it’s because they were thinking about you first.”
This is a truly disturbing idea, if you allow yourself to look at it as more than, ‘Awwwww, they’re soulmates — how cute,’ or whatever the writer of the example meant. What if you’re ‘thinking about someone a lot’ because you’re afraid of them? Don’t really want them ‘thinking about you first,’ do you?
Also… by what mechanism would you become aware, even if only subconsciously, that this person is “thinking about you first”? (That’s a serious question; I’d love to see a serious answer, although I don’t expect one. I just want to make fans of “Psychology” admit that they’re using something they know is impossible to “explain” a pet conjecture.)