Should I Let Him Go ?

I'm currently in a relationship , the bad part of it its that we are 1633 miles away from eachother .my sister told me to let go because I don't really know if he's cheating on me and all that . I don't know if there's any chance for us to met in the future who knows .. Or I don't know if relationships like that actually work out .. I'm so cinfused . Sometimes he texts me soo late , but it's because he plays a sport or the time is different here then there . But sometimes I feel like I'm not really in a relationship :(. Please help...