Try joking with him. If you guys are friends, you can dump him as harshly as you want if you end it with a smile. By regularly pointing out that you love your boyfriend and that this guy is your buddy. Never quite striaght forward, hint it well. like:

"Oh you know I miss my boyfriend SO much! He's my heart.. . etc"
"I'm so glad that I have a friend like you. We'll be friends forever right?"
"You're the coolest friend a girl could have, I'll vouch for you to your girlfriend."
"Oh, I have this friend. . . She and I have different tastes, but I think you're her type. . ."

And the like