Dr. Jacqueline B. Sallade offers ideas for maintaining your mental health.
Trust is the basis of all good relationships. Even love isn't enough without trust. Yet, no one is totally reliable, and no one remembers everything said or never chnages her/his mind. Humans are inconsistent,fallible, make mistakes, and change. So, there needs to be some tolerance, flexibility and evolving standards. There's a point where forgiveness and repair work. But, that said, repeated and unresolved infidelity, addiction or abuse destroy trust to the intolerable extreme.
What about the smaller bouts of mistrust which develop though? He doesn't bring back the groceries he promised to buy. She doesn't keep to the financial deal they agreed on. He violates their implicit sex contract with his avoidance and does nothing about it. She changes her mind about her work schedule or volunteer work. Where's trust then? Without some negotiation, and these issues often go unaddressed, slow deterioration of trust grows. Maybe there's enough good stuff happening that the relationship retains a good comfort level anyway. Maybe the couple just becomes less deeply connected, resentful and superficially Ok but not really happy. Better yet, they could address the issues, learn to compromise and accept change and move on in a healthy way.