Communicate frankly with your partner. Acknowledge that the relationship is on the rocks and that both of you want to rekindle it. Decide what needs to be done to save the relationship.
Take action towards change. Change your routine. Keeping things the same every day may make the relationship dull. Find ways to surprise your partner or just try new hobbies together. Take a vacation.
Take some time off from romance, or time off from the relationship altogether. Spend time apart and the later reunion will be all the more special.
Stay calm through this period. Fear or paranoia will only make the situation worse. Also, whatever you do, don't fight with your partner or yell, as such things will only quicken the relationship's demise.