My boyfriends ex

Is it normal to feel kinda jealous of your boyfriends ex? Like she got all this time and attention from him once... and it sucks even more when she tells you about it... From what my boyfriend, friends, and even the ex herself have told me, she was a really shitty girlfriend and I've been dating my boyfriend about 4 times longer than she did, but it's still kinda unsettling... how do I get over this feeling