To control stress in a relationship, first define the problem and relate is to each of your problems as feedback. Then, identify the specific conversations and action patterns and take action to neutralize the hidden causes. Learn to communicate with your partner about it so that you may help solve the stress.
What Janadu said is true, if yer expectations aren't to high then if they do something that you don't like, it wont bother you to much, and if they do something you do like it'll be all that much better. But when all else fails? I find going a few rounds with a good old boxing bag helps a lot.