I know it sucks. But you're young, and I know that sounds dismissive, but you're young, potentially single and at uni. This is the freest with the least responsibilities you'll have for the rest of your life. Not saying don't work hard in school. But no need to be locked down. Meet as many people at school as possible. Be with as many girls as possible, respectfully and consentingly of course. 19 is super young too. No one's perfect. This time in your life is for making mistakes so when you get older and they have more impact you won't make as many. Get on a dating app and go get food with someone new. You can always end back up with the girl that cheated if it's worth it to you... But I think you should take the opportunity to get out there and meet as many new people as possible.