Is there a way to love somebody less?

I don't think so.  The only cure for love, I have found, is time and distance.  The more you fill your life with other people and other things (job, hobbies, outings) the less time you have to dwell on that person you love.  It slowly dulls, becomes less intense.  But love rarely disappears completely.

There's a way, replace him with someone else who is even nicer and better qualities than your ex-boyfriend.  In time you'll forget about him or the emotions that you used on him will be a lot lesser.