A guy told me he's in love with me and I don't feel the same way. What do I say?

You can say, “I really care for you too but not in a romantic way” and “We each have our own lives now that we live apart.” In other words, be honest but gentle.

I’m with @janbb – I think you gently discourage him. Basically, you would say – “I’m glad you like me, but you’re now far away and I don’t have the same feelings for you. I don’t know you well enough to see if we could fall in love.”

I realize that you’re trying not to hurt his feelings, but sometimes the truth – painful as it might be – is the way to handle the situation.

You could hook him up with one of your friends. That would be totally cool.

“I’m sorry, but I can’t say the same for you.”
And maybe it’s time, since he feels that way, that you go your separate ways.
Honesty is always the best policy. (And some things are better left unsaid.)

He just moved. He is lonely, and thinking about who made his time “Back home” very cheerful.
He believes he is feeling more than he is, most likely. Do you want to stay in touch? I get the impression you do. Either way, you need to tell him you don’t feel that way. Tell him that you enjoy being in touch (only if it is true), but that love is not in your heart. He needs to know how you really feel. He also needs you to be gentle. Moving is tough. It is a shock for most people, even when it is what they want.
Point out to him that making new relationships takes a while. Tell him long distance love is too tough to keep going, and besides, when he meets a girl there, he would have to face telling you.
Poor guy, he’s at an age when people are falling in love (some several times a day), and the desire is there, but he is new, and doesn’t have relationships formed there yet. You are his strongest alliance at this time. He is in pain, and reaching for the closest girl he has.
He needs you to care, but he also needs the reality that it is time to make some friends where he is. You should discuss it the next time there is a phone call. He will need reassurance from the tone of your voice.

Exactly what @janbb said. Wouldn’t you want him to be straight with you if the shoe were on the other foot—even if that hurt you?

You can use the expression that woman have been using for years. “I’m flattered but I like you as a friend”. honesty is the best policy, it’s better not to string the poor guy along.

Just Say No. We don’t know the tone of the relationship, you do. You figure out the best way to say it. But say it as soon as you can, and tell him you couldn’t say it any sooner because you were too surprised.

I would back off contact.

Nothing like punishing the man for being honest. No wonder why men don’t say I love you anymore. it costs a friend to be honest.

Well, it could mean he’s getting a little obsessed. Even the OP expressed the thought that it didn’t really make sense. Just not a good thing.

Just tell him you don’t really want to be in that sort of relationship, and that you are better off as friends, and you hope that doesn’t make him upset with you and that you love him as a friend. No reason to be brutally honest, gentle and honest is the best sort of route, just don’t sound like you are trying to make it a joke or blow it off. It’s rather important to address theses things before people get the wrong idea.

Yah. Tell him how you onestly feel.

Tell him you wish to just be friends. It isn’t really fair to either of you if you don’t feel the same.