Doing things that damage your ability to connect and form a stable attachment with someone else sexually -- that's serious damage. It's like taking a GPS device and smacking it a couple of times with a hammer: it may lose its proper directionality, which is outward, toward self-giving love. If you knew that, and you did it anyway, it actually could be spiritually serious.
Madam, I do not need you to elucidate me on the nature of mortal sins. My comments to Hunter112 were more of the nature of pure philosophy and ones ability to come to terms with faith and catholicism.