You do know that the brain releases different levels of hormones from masturbation vs intercourse, right?
pubmed.ncbi.nlm.nih.gov
Our biology has evolved specifically to reward sex with others over self pleasure. You're a moron if you don't think our brains have evolved to differentiate self pleasure from sex with another person. "It's all in your head" is a retarded way to brush it aside. Of course it's all in your head, literally everything you experience is in your head you fuckin retard.