See when masturbation is the expression of yourself --no pictures no desire--natural expression like a child getting a hard on--all cool
the same with sex with a partner
in fact--in this expression--no touch even necessary --as it is simply self expression and not dependant on another person
the pictures and experience you are having is addiction-- addiction is something dropped through self will and breath in the moment--thus will and breath--and if you walk as the breath--it is only the moment to transcend--there may be several moments following each other--yet it remains only one to direct at the moment of direction--thus--the simplest way--to will and remain self honest and directive
Best is to do the sexual expression experience with some-one also walking with you and are willing to explore self expression beyond the ideas of how this normally is done
you will find penetration to be rather lacking once full self expression is effective
What is an amazing experience is sexual expression after an intense extreme self honest self forgiveness session that was done with equal passion--then you discover what is self movement--that which cannot be contained