People who have self-confidence issues and who feel that they are inadequate in certain areas often feel that they are not even able to hold on to a pleasant relationship. They often exaggerate tiny problems or they imagine ones that do not exist. They feel that they are not the perfect one for their partner, and that they should find someone else instead of wasting their time on them. They also tend to look at their partners as saints who have decided to stay with them in spite of all their inadequacies. They tend to think about their mistakes as the final straw for their partner, who will leave them after that. They think that a mistake is the end.
They never forget about their mistakes, even if their partner already did a long time ago, and they cannot let go of their guilt. They cannot see themselves as positive people, no matter how hard their partner tries to convince them.
If might be hard, but the only solution is to teach these self-loathing people to forgive themselves and to accept that everybody makes mistakes, and the key to solve the problems that they have created is to recognize, regret and rectify them, if they are really serious. If they are minor ones like forgetting about putting gas into the car, then they should try to get over them as soon as possible, since their partner does not care about them, only they do. Their partner should let them know that they also make mistakes that self-loathing people forgive, so why should the ones that they do matter anyway?