Tough situation. But you have to protect yourself.

I had to face this with a couple people who were just using me. They were draining me of energy at a time when I couldn't afford their vampire-like behavior.

I simply told them, "I can't do this anymore. Try to understand." And I left it at that. If they kept trying to pester me, I would either ignore them or repeat what I'd said earlier.

It takes determination and resolve, but you can do it.

Sorry to seem so cold, but sometimes you have to harden your heart a little.
Nobody likes rejection (I ought to know, I've had a ton of it), but eventually, they get the message.