I’ve said before that relationships suffer from the bias that "We tend to remember slights and frustrations more than favors and kindnesses." More now from Marginal Revolution:
Immediately after one person performs a favor for another, the recipient of the favor places more value on the favor than does the favor-doer. However, as time passes, the value of the favor decreases in the recipient’s eyes, whereas for the favor-doer, it actually increases.
Remember that when you accuse someone of looking at their partner(s) with excessively rose-colored glasses.