Lust is a sin. If you masturbate to relieve your lust after someone. Then IMO maybe... Yes. But in KJBible it also comes across that if you think of another woman in a sexual manner an ponder sexual acts an she is not your spouse you have already sinned. There is a verse I'm thinking of, but i don't know it right off. There is seven "deadly" sins. Or "cardinal" sins. I think they are Lust, Greed, Gluttony, Anger, Sloth, Envy, Pride. An if the shoe fits.... An one other thing in the bible says that you shall not covet another mans wife.