Every time I talk to my best friend on the phone I masturbate. Help?

[Erick r]

I am male. She is female. I love her sooooooo much. She knows this and we are as close as you could possibly be without actually dating. Needless to say, things are complicated between us. I am more concerned with why I can't ever talk to her on the phone without getting horny. It's like a natural response I can't control. I don't even notice it happening. I am holding a conversation with her and I am immediately horny and one thing leads to another. I never let her know what is happening because I am ashamed I can't keep my hands to myself, but I can't. I have never had this problem with anyone else. What does it mean? Is this normal or somewhat normal or does it have a documented psychological meaning? Please try to be as serious as you can with your responses. I know it seems silly but it is not. I really am in love with her and wonder if that is what is causing the problem or if it is completely sexually based. I will leave with one last detail. We have slept together and she is the best sexual partner I have ever had.