I think honesty can keep the trust from being broken. One's trust doesn't get broken because an SO leaves or loves someone else as much as because they start it behind one's back. My husband told his ex right away when he started dating me, did not hide it or let it get to her ears from someone else or wait until she "discovered" it. His ex and I are good friends and she still trusts him. I trust him because I watched how he treated his ex, mother, my mother, etc., the other women in his life.

I can't imagine, were I cheated on, that I would want to regain the trust. Someone else can't "accidentally" cheat. In my marriage there would have to be really broken communications for that to happen and I don't see that happening. If my husband met someone else, he'd tell me right out, would choose one or the other and keep it clean and keep me in the loop as to what was happening.