So you've been with someone for a long time, maybe even for the better part of your adult life.
No one has done anything to disrespect one another. Time has passed leaving his marks on your face, on your body, on your soul. Maybe you've grown weary of one another, maybe you've grown apart, maybe everything you're doing now seems trivial and deprived of meaning, of essence.
If you've always been right to each other, if you've always been respectful to each other, if you've dedicated your life to each other, don't be stupid now. Doing something frivolous, allowing yourself to fulfill a whim, see if you still have "it", won't change anything more than a couple of days or weeks of your day to day routine. Another person won't change your life, it might break the rut you're stuck in for a while, but it will definitely break more than that. If you are feeling stuck or bored, don't change the person you are with, change your life together. Go for a long trip, take up a new activity, remember everything that made you fall for each other, learn to have fun together again, don't change the person, change your perspective, communicate, ground each other, learn to hold each other and walk hand in hand forward again.