How do you tell someone you don't love them anymore without seeming uncaring?

There's a difference between love and romantic love.

Real love cares equally for the well being and happiness of [i]both[/i] self and other. It knows the other realistically and accepts the whole person just as they are.

Romantic love is an illusion which rarely lasts longer than a couple of years. It thrives on mystery. Not fully knowing the person, the lover projects, believes in, and passionately loves only an internal image of the beloved. The more you get to know him/her, the more the illusion falls apart.

Breaking up with someone you no longer love will definitely hurt them if they still love you.
But it would hurt them far worse to stay in a relationship when you don't love them.

Real love, which grows slowly, can only be built on mutual honesty.

So you're wanting to move someone into the friend zone don't do that it hurts worse than you just saying we've grown apart and send him his own way and you go yours

By NOT saying anything, ever again.
Eventually they will Catch On.

Gently