How far is too far during the betrothed

Some that are betrothed feel that they are now free to be alone and even free to indulge in french kissing. They speak and act as though they have been made as one already without a marriage ceremony. According to the scriptures we are to avoid EVERY appearance of evil. As they are not married yet, why indulge in that type of kissing which almost always results in a desire to go further. If we have been instructed by our God to \"be ye holy\" should we not be careful that we don\'t offend a holy God? 
 
[JPL's response: Amen. Such rationalizations as you describe are an abuse of a beautiful pattern God intended to protect from these very compromises.]