saw my ex in public and need to complain

i don’t know who to talk to about this or if it’s even something i should talk about. it may be silly but i just saw my ex boyfriend in a walmart and i can feel myself spiralling into a panic attack. for background information me and him dated for a year and a half and only broke up a few months ago, he dumped me because his friends were telling him lies about me and he believed them over me. i just went shopping with my friend and we saw him picking out flowers and valentines cards, the reason that hurt so much is because when me and him were together on valentines he told me all that stuff was a waste of money even tho valentine’s day is my favourite holiday and gifts are my love language. during our relationship i put up with a lot more than i should’ve because i thought he was incapable of being romantic but now i see him with the girl he found a week after we broke up and he’s doing all these romantic things that he refused to do with me. maybe i’m selfish but i hope she cheats on him.