There is venial sin and serious sin which may be mortal sin. Mortal sin is usually only known to God. Serious sin is often apparent to everyone. The in your face homosexuals and people who divorce and remarry as well as abortionists etc. are in a continual state of serious moral wrongdoing and serious sin.
Forgiveness requires sorrow for sin and amendment of life. “Go and sin no more.”
The divorced and remarried must go and sin no more just like the rest of us.
Not a good idea for sinners to pick apart various sins and judge which ones are worse than others. Jesus said if you have anger in your heart you have committed murder. Pretty tough stuff. Is someone that re-marries worse than than a murderer? I say leave such judgments up to God.
And by the way in regard to “Go and sin no more” there is no such thing as a mortal man not sinning any more as long as they live on this Earth.