why do i feel this way

i should be over my ex we didn't last for very long but we did do alot as a couple. Whenever he pops into my mind while im eating I literally feel sick or just my appetite goes away or whenever im on my phone just scrolling all happy and shit cause of funny shit or postitive stuff then he pops into my head it literallt makes me so sad.. I want to text him so badly but I know I should and I'm not gonna!! :((