The way I see it there are four scenarios that could occur now:
1. He tells ex you like her, she still likes you, you end up back together (before breaking up later because don't date your ex twice, man)
2. He tells ex you like her, she doesn't like you, you both avoid talking about this because it's awkward, so whatever.
3. He tells ex you like her, you completely disregard anything that happens next because you're going to college in like three months and will be SURROUNDED by 9s and 10s everywhere all the time
AND FOUR: He tells ex you like her, you make it a WAY bigger deal than it needs to be, try to explain to her the whole deal, get super awkward, probably stumble over your words, wish you were never born, crawl back into bed and never get out of it because the G-forces of cringe will keep you pined there.