Building and maintaining trust requires making and keeping agreements. If you realize you don't want to continue the agreement you've made, discuss it with your partner. Don't undermine the agreement or be miserable. When you feel angry that your partner has let you down, ask what his understanding of your agreement was.
Good agreements bring stability and predictability to the everyday world of a relationship.
It's great to feel you can count on a partner, whether it's to take out the garbage or to safeguard your petunias from the neighbor's dog. But some agreements should not be made. The first is the kind that people feel obliged to make. The second is the kind that people don't really plan to keep. The problem with this is that your partner will be counting on you to do the thing, when you haven't really committed to doing it.