How do I tell someone how I feel if they are moving?

Telling someone how you feel before they leave might be a release of a burden off of your shoulders, but it might put one on their's (whether you meant to or not). I might suggest that you use these last remaining months to really let them know that they will be missed and make sure that you have solid means of communication set in place for once they move away. So perhaps their moving won't be the end of your relationship or the relationship that could be!

:) hope that works out for you!

Are you dating? If your dating, you should definitely tell them. If your not though, still tell her but maybe don't lay it on as heavy. I had a friend that told me he was really sad that I was moving, and I thought it was really sweet!