I didn't think the ending was that confusing. Im guessing Megumi is in college somewhere else and they are still in constant contact indicated by her roommate remarking if the letter is from the girl Megumi is always talking to. I think the ending implies they are still together albeit really lonely being apart. Long distance relationships suck.......I know for a fact :) (turned out well though!). I guess it's a weird bit of realism in our fiction.