Why does it hurt?

my friends came down to tell me today that they saw my ex with his new girlfriend. i told them it didn bother me but i realised i was upset when i got back in this evening from work and started hoovering (i'm not a fan of the hoover). i guessed he was seeing someone else when we broke up but i had no proof. i don't even want him but it hurts that hes with someone who isn't even all that. not saying i'm the hottest thing but i'm pretty hot (lol) and b4 u even go there i have a pleasant personality. i'm over him but why do i still feel a bit bruised?