I'm well aware of Rome's non-Scriptural man-made contrived "mortal" sin requirements.
Your wife asks if the dress makes her look fat and you lie....it's a "mortal" sin.
Rome has tried to minimize some sins compared to others.
“That dress makes you look fat,” is an opinion statement, not a fact statement. “Fat” as an appearance quality, rather than as a type of flesh, is a matter of opinion. Then there’s the issue of “the dress makes you ...”. If the viewer already considers the questioner “fat,” the dress isn’t doing anything. As the Irish joke says, “Do these jeans make my butt look big?” “No, chocolate cake makes your butt look big.”
Therefore, this situation is not one in which “lie” is a useful verb. It’s a question of determining the subtext of the question. Some options:
“Will you reassure me that I look okay for the planned event?”
“Is this dress the most flattering to me of my available options?”
“Do you think I’m fat?”
The answers depend on one’s character. A decent husband would reassure his wife. If the dress has a rip, has a stain, looks awful with those shoes, etc., he would tell her. A perceptive husband might say, “That one’s okay, but you look really slinky in the blue one.” An unutterable cretin would say, “Yes, I think you’re fat,” and flatter himself that he never lies.
Hardly. Do you even know what the term "mortal sin" means?
Baloney sandwich plus pickle.
Nothing in my vast experience in the Church supports that assessment. Perhaps you have been misinformed.
Actually, while all sin is sin, and is mortal in the sense that one sin will send one to Hell apart from saving faith in the Lord Jesus. and whosoever shall keep the whole law, and yet offend in one point, he is guilty of all" in the sense that he is "a transgressor of the law," (Jas 2:10,11) yet just as there are "weightier matters of the law." (Matthew 23:23) so also there some sins are weightier than others.
Thus there are different penalties for sins, and not all sins are capital offenses in this life, while there are different degrees of punishment in the next.
An adulterer is to be executed under the Law, (Deuteronomy 22:22) while using another man’s field to feed your animal meant you had to make full restitution. (Exodus 22:5)
Likewise, in this life there is a sin unto death, versus being delivered from it. (1 John 5:15-17)
In addition, in the final judgment, besides being damned due to rejection of Christ, the dead will be "judged out of those things which were written in the books, according to their works." (Revelation 20:12)
And in judgment there are different degrees of guilt, relative to the light and grace on is given, which determines the degree of punishment.
And that servant, which knew his lord’s will, and prepared not himself, neither did according to his will, shall be beaten with many stripes. But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more. (Luke 12:47-48)
Therefore. those who received greater blessings of light and grace are more accountable for sins:
And thou, Capernaum, which art exalted unto heaven, shalt be brought down to hell: for if the mighty works, which have been done in thee, had been done in Sodom, it would have remained until this day. But I say unto you, That it shall be more tolerable for the land of Sodom in the day of judgment, than for thee. (Matthew 11:23-24)
Thus we see that whileany and all sins are spiritually mortal in the sense that "the wages of sin is death," (Romans 6:23) yet there different degrees of wickedness and punishment, which is also relative to the light and grace given. And with believers being the most accountable. (Hebrews 10:19-39)