I need advice on how to lose feelings especially since I’ll see her in school

I was and still am extremely upset about the breakup I liked her for a year I tried my best but she didn’t feel I put in effort as I was pretty shy to her and looking back she didn’t even try in the relationship but it’s fine I guess.

but school is starting back and a lot of my class mates still think we are together and will probably tease me and another thing is in my old classes we all were in a mini well group we were all friends so it makes it even harder knowing I’m gonna see her a lot in school and I don’t know how to feel.

I don’t wanna be a self proclaimed depressed guy as I’ve never been diagnosed however Ive felt sad and miserable for the past two years but enough of that I’ve recently started improving myself but it hurts knowing she moved on from me in less than two weeks as she got with someone new pretty fast and completely forgot about me.

I just need advice on what to do when I see her in school without feeling sick.