Is it easy to stay liking someone for a year, if you know you're not going to be seeing them for the next year?

Don't think too much about your relationship with any one person who isn't there when there are others who are, simply wait until they are back and accept them as they are, they may be a different person to the one you knew before just take life as it comes, don't worry about things that may never happen, enjoy what is without worrying about what the future has in store for you.