Of course it hurts, that's completely natural. If it helps, I read an article in a girlie magazine once, written by a guy, that said women always get upset when they see how their exes are doing after a split, thinking that because they've gone out, got drunk with their mates, slept with a floozy and boasted about it to anyone who'll listen the next day, they're over it. But the author said that this is in fact the male equivalent of sitting at home, listening to Damien Rice and crying into a pillow. Just because your ex is giving the outward appearance of having moved on, doesn't mean he has. In fact it could be a dead giveaway to how much he's suffering - he is missing you so much he is literally looking for a replacement 'you'. Can I ask why you broke up if it was so traumatic? Is there no way you could try asking him if he'd want to give things another go?