Most Helpful Guy
Because he wants to have sex with other women and have you as backup sex.
Most Helpful Girl
Probably he wants to have his cake and eat it too. As in he wants to have you there to fill his needs (what ever they may be from companionship to having sex) but at the same time he wants to be able to date other girls and enjoy the benefits of being single. DO NOT GIVE HIM THE GIRLFRIEND BENEFITS WITHOUT A RELATIONSHIP IF RELATIONSHIP IS WHAT YOU WANT!!! And I mean that!!! One could think "but how else would he change his mind about it" but that's sooooo not how it goes. Why would he want a relationship if he gets what he wants and more without being in one, without having any responsibilities. Not saying this is what you're doing but just a warning.
When/if you're honestly fine with being just friends with him and don't feel like you'd want anything more (+he's not trying to get anything more) and don't mind him dating and sleeping with other girls, then there's no problem (well maybe ask him to cut the babe stuff if that's bothering you). Before that I'd suggest backing off, trying to move on (even if that wasn't what you want at the moment, it's way healthier than staying stuck on something that's hurting you), heal yourself and let him miss you.
Take care! ❤