Looks like he is not a happy person to me it might not be relationship but something else that must be bothering him deeply which he doesn’t want to share.
See if u can be frns with him if u really like him, if he is happy with other girl I t hink fir his happiness u should let him go no matter what , that’s life and by doing that u will be a bigger n better person. I know being let down hurts but it’s just that it’s for your good. Learn from ur mistakes n continue to be positive u will end up in something that will last for lifetime all the best and cheers 🙂