is it a proverb or no?

[Zainabr]

hi.do you know the meaning of this sentence?is it proverb? he's just not that in to you

[Jamie (K)]

It's not a proverb. It's just slang that means, "He's simply not interested in you." "Into" is often used to mean "interested in", so we might say that someone in "into hockey" or "into cooking" if those are activities they enjoy.