If you are in a bad relationship at no point should you think to yourself "I'll wait until they feel the same."
If that day never comes, you've convinced yourself to stick around against your own happiness. Or that day could come, but you've had a change of heart, making the break-up more harmful. If you ever feel that there's nothing keeping you two together, then there's no reason for you to stick it out, odds are they feel the same way. Otherwise the break-up will be far messier than if you wait, because not only will feelings be hurt, but you both will have lost time to both get over it and move on.