I'm not sure if this actually refers to the relationship rather than one of the people involved in the relationship. The Knight of Wands is fiery, darting off after adventure with flames streaming from him. He's very hot sexually and temperamentally. He blazes in and out of situations. He throws himself into something only to throw himself equally quickly out of it before he has to take on any responsibility or commitment.
Some people refer to this Knight as moving house or moving away from something. I think it depends where he is in the spread. For example, if he is facing or galloping towards another court or a situation, he is coming towards you. If he is galloping away then he is getting away from you. He is akin to a flickering fire with very little fuel and he will burn it up very quickly.
He is good or bad depending on the situation. If you or another are more a Knight of Pentacles, slow and plodding type, this Knight could be advising you you to jump in guns blazing. If you are hot headed and inclined to let your temper get the better of you, this Knight could be advising you to temper yourself and not act on impulse. To think things through.
As you can see, he is all fire energy. He is sexual, hot headed, a real fiery torpedo which is great if you only want a short term fling or a lover. He does not bode well for a long term relationship or with someone you want to stay the course with. You would be better off with the Knight of Pentacles.