When a mother has this protective love for her son she becomes fiercely protective of his life, crippling his emotional growth and tying him to her apron strings as 'Momma's Boy.' This tendency has been documented even from Biblical times in the story of Rebekah, who encouraged her favorite son Jacob to steal his brother's blessing through impersonation.
If you are not married but you're in a serious relationship that is headed toward marriage, where do you draw the line on physical contact? Do only what you would do in front of your father. If you can’t relate to that because of a broken or unhealthy relationship with your natural father, substitute spiritual father. If you wouldn’t do it in the presence of your pastor, don’t do it.