It's more than some guy self diddling, it's about what constitutes Cheating on a spouse, to say I personally don't like it but if my wife Husband do it, I'm cool with that, it's their choice......BFS!
When that becomes ok in a marriage, the one watching the inappropriate content is effectively leaving the Marriage for greener pastures.
1Co 7:2 Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband.
1Co 7:3 Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband.
1Co 7:4 The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife.
1Co 7:5 Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
In Marriage we take a VOW, to our perspective spouse, and to God, have we as Christians forgotten what a Vow is and means to God?
Num. 30:2
If a man vow a vow unto the LORD, or swear an oath to bind his soul with a bond; he shall not break his word, he shall do according to all that proceedeth out of his mouth.
Deu. 23:21
When thou shalt vow a vow unto the LORD thy God, thou shalt not slack to pay it: for the LORD thy God will surely require it of thee; and it would be sin in thee.
Ecc. 5:4,5
4) When thou vowest a vow unto God, defer not to pay it; for he hath no pleasure in fools: pay that which thou hast vowed.
5) Better is it that thou shouldest not vow, than that thou shouldest vow and not pay.