While it's impossible to read people's thoughts, I try to put myself in the other person's shoes when I'm talking to them. If I think someone can handle the honesty, I'll just shoot it straight and politely inform them that I'd rather not maintain communication. It doesn't have to be mean, and it doesn't have to hurt. Just talk to people like you'd want them to talk to you.

If you feel like the other person might take the news badly, try to be more delicate in your tone, but you still need to be honest with them about what youre feeling about their companionship. It doesn't help anybody to lie to them, just be a little softer.