It can work, but it also cannot
It can get really painful when the other starts to see other people or showing any signs of getting over it like going on vacations without you, for example. You can still be friends, but maybe is a good idea to give some time between you two so you can work though the break up on your own and then try to restart as friends when these feelings are less intense. He obviously isn't over you yet.
OT: I did, but the guy wasn't exactly a boyfriend. Anyway, it lasted for like two years, but then he became really annoying and toxic so I ended the friendship and never saw him again.