Oh God no, do it immediately. Tell him you understand that it hurts him and that's the last thing you want to do, but you can't be with someone you aren't committed to and you want him to be with someone who does feel that way - try to put it across in a way that benefits both of you.

If he threatens suicide, ask him to please call a suicide hotline or speak to a friend. I understand you will be worried, but he is trying to manipulate you (even if he is doing so unconsciously). If you know where he lives and he threatens suicide, you might consider calling the emergency services. Then you will know that he is 'in the right hands' and you can take leave of any responsibility you feel towards him.

I've been there - couldn't leave a man I didn't love because I was afraid he would hurt himself. The guilt was awful. But this is not your responsibility, you need to live your own life.