What if it went something like this:
Hae approaches Adnan's car, realizes Jay is driving.
HAE: If you don't tell Stephanie that you cheated, I will.
JAY: If you do, I'll tell your parents you've been lying to them for years and having sex.
HAE: Then I'll just go to the police and tell them you're a dealer.
See how the situation could have escalated? Especially if Jay was involved with some higher-up suppliers who could retaliate if he was ever arrested or questioned and they thought he snitched at all.