Alexandra at yourtango.com writes about five quiet relationship-killing behaviors. One way to alienate your partner is to express more criticism than appreciation. Reminding your partner of past mistakes, despite positive changes, can take a toll on a relationship. Untreated depression can cause problems for couples. Expecting perfection from a partner can also lead to unrealistic expectations.
An interesting read which is definitely worth your attention:
Five Silent But Deadly Relationship Killers