Most Helpful Guy
OK, this is tough, but the worst thing you can do is to avoid him or keep him in suspense because that's not letting him down easy.
I think ultimately, the truth will be the best and what he really needs to hear.
Your only other option is to give him a half-truth or white lie, like telling him that there's someone else or that you don't want to risk your friendship...but ultimately, these half-truths are never as good as the full truth.
Now, how to actually tell him...
Since you've been in this position yourself, I'd start by telling him a story of what it was like for you, and then just tell him that you're in the same situation with him now.