Yes there is a real harm in it.
You look, then after a few weeks someone catches your eye or its become mundane agan and you pick someone who isn't your taste so you can be assured to keep them at arms length.
You message each other, then the excitement of the messages aren't enough or you convince yourself this person could be just a new friend.
It develops into an obsession and you are mooning over the site/person and your behaviour starts to change.
you are now either embroiled in a full blown or emotional affair, living in fantasy land oblivious of the way your behaviour is now affecting you parnter and children as you have emotionally withdrawn from them to invest more time and energy in this.
Final stage you convince yourself the grass is greener even though you know deep down it isn't and get careless. Your partner finds out and is devastated at the betrayal, even if you haven't met face ot face or laid a finger on another person you have kept secrets from your partner during this time and treated them like something you scraped off your shoe. You do this to justify your behaviour to yourself, pushing them into reacting so you can run away again into your fantasy when they react negatively.
Your partner is distraught and disgusted in you that you have abused their trust so lightly out of boredom and the relationship breaks down. Your children now have to go through access arrangements and the financial breakdown of a relationship all because their mother didn't have more imagination when picking a subject to entertain themselves with.
Why do you feel this way?
Is it just your relationship or do you feel bored with life in general?
Widen your field of knowledge either through a club, hobby or more education. Take up mountain climbing, sky diving or anything other than this.
If at the end of all this you come back to the point that it is your relationship, try to work on it out in the open together you may both feel in a rut and going through the motions.
If that doens't work then look to end it.
All of this is less painfull than what you are contemplating.