ex girlfriends

Jessica
Hello ladies need some advice ☹️
Is it true you can be just friends with an ex? Nothing more? My boyfriend seems to think it's okay to be friends with his ex girlfriends and doesn't like them anymore than just friends. However I'm very uncomfortable with it because I found out a while ago that he has been in boxing two of them when he is drunk asking them to hangout and one even gave him a lift home and I didn't find out until 2 months later when I stumbled across an unknown number in his messages. He keeps saying nothing happened, not sure I believe it because this chick is obsessed with him and he was super drunk at the time. thanks for listening