In love with my sons best friend

I am married and lost my son four years ago,and his best friend has been there for me the whole time ! I became quiet dependent on him to be there for me no matter what,and over two years ago I realized that I wanted him so badly and I could not make these feelings go away even if he would let me just hold him hug him.I just want to be close to him.I know I have never been in love until now and I have to have him it is making me crazy ! I told him how I feel and he told me it would never happen he would never have sex with me or anything else.I don't want to live without having him how do I get him to change his mind??