You need to let him know that you consider him a good friend but you're not in love with him. Being with him in a romantic relationship just because he loves you would be damaging and unfair to you both. In the end you would end up resenting him and lose your friendship as well.

It may be you won't stay friends so that he can move on, but perhaps someday you will be friends again. It is better to be honest. I know this from experience.