How to forget the girl you love?

I had a going relationship with my girlfriend and because of some private situation of her I had to break up. It was ultimately the right thing to do for myself

I was genuinely in love with her and she is my first ever gf/ someone I had emotions for.

Whats done is done but the problem is, as it turns out, suddenly breaking up with yout lover stings A LOT. My life have been ruined for 2 days now. Whenever my head is empty I think of her automatically and cant undo it.

Also cried which happens annually at most

So guys what should I do in a situation like this? Also she is in the same school with me and the breakup was very smooth since we both (hopefully, I dont know the scale of feelings she have) could see whats coming and had nothing to do to stop it.