You are correct Sister T. God will forgive us, the problem comes when one continues to promise to change but fails to keep that promise. A person has to make a decision to permanently change and make no excuses for anything there after.
I realize that some folks are repeat offenders--but even God forgives the repeat offenders. A person who truly repents with turn from their old ways. If they mess up, they turn around again, and keep making efforts to live a righteous life.
The problem comes in when our expectations are too high of the person, specifically marriage partner, is trying to change. When he/she messes up again, we are ready to bail out. Sometimes it's not totally his fault that he fails, sometimes we share in our spouse's failure. Why---because we never trusted them to do right from, we never trusted them to succeed, we never truly forgave them for their actions.
I really can't expect my husband to do the right thing, if I don't fully forgive him after he messes up. For instance, if he were to have an affair, I must forgive him, wipe the slate clean and move forward in our relationship. There must be restoration---placing the relationship back to where it was, actually even better.
When I say that I don't trust my husband because he did it before and I'm being cautious, then I am actually speaking a negative thing over my marriage. We are one flesh when we become married. Therefore, If I don't forgive him the way God intends for me to forgive, then
I am an accomplist to his failure if he was to mess up again. The Bible says as a man think in his heart so he he----if I think my man is going to mess up again, then it probably will happen. I am guilty of thinking my husband would fail---so why should I be surprised when he does,
I counsel many marriages, and I see one in the relationship say
"I knew he was going to do that again, he always does it." Well, that tells me that you didn't wipe the slate clean, and you expected the worse for yourself. Why be surprised that you got what you expected.