In some cases, a habit remains, which is still likely not subjectively sinful <==This statement is false;
although it is hard to tell what he is saying since he used the word "subjectively" instead of the clearly applicable "objectively". The use of subjectively sounds like an attempt to bring relativism into this.
The act itself is a mortal sin and can be forgiven as with other sins.
Do you know the difference between objective and subjective sin?