If one partner has lost interest, move on. Why would you want to be with someone who is not interested?
But on the issue of long distance relationships, I can offer some advice. I married my high school sweetheart after a 5-year separation because we went to colleges in different states. I think it lasted because we stayed in constant contact via phone calls (back in the day of long distance charges) and mail (snail mail). Today, with email, Skype, and free phone calling, it should be easier than it was for me and my guy.
Then we had an Army marriage for 20 years that averaged him being gone every third night. We made use of the same forms of communication again.
The bottom line is we loved each other, no matter what, in good times and bad, and forgave each other over and over when we didn't like each other very much.
If the love is there, you can overcome anything. If you don't, or he doesn't, move on. It will never work.