he may have been with a lot of other people before but its obvious he wasn't happy. they didn't care about him enough to stay with him either, otherwise he wouldn't have to call so many different people to keep him company.
and as for shun, he doesn't somehow deserve her more than dai or anything just because he likes her so much. that line of thinking is a little creepy, to me. she doesn't owe him anything. that being said i like him, and he did his best but needs to move on. he's a very good guy and will definitely find a lot of happiness in the future.