Videos on iPhone photos don't play?

So I decided to sign up for iCloud backup so that I don't lose my photos. But whenever I want to show someone a video (when I have no Wi-Fi) it doesn't load. In the bottom right corner there's a 'loading' sign and even if I 'load' the video when I do have Wi-Fi it still buffers without Internet connection. I have tried to delete iCloud but it tells me that I can't keep my photos unless I download them to my device, and I don't have enough storage to do this help?!

Sdsd