How can you let go of your love for someone and still remain friends?

He bounces in and out of my life and seems to think that he can manipulate me easily because he knows how strongly I feel and how much I care about him as a person...the good and the not so good sides of him. It makes me truly happy to be around him and spend time with him, but I always seem to fall into the same old traps. I value his friendship and don't want any more "head trips" or uncomfortable moments. I certainly don't want to be used. He can be so wonderful when he puts his mind to it and I would like to work things out remain friends first and foremost....meaning helping make each others lives a little easier and being "chill". Tell me please...how does one work through past baggage and live in the moment with acceptance and honest caring.