What should I do if my husband always doubts and insults his wife for no reason?

This is not your problem anymore. It is basically certain that your husband has a problem, either psychologically or with his character. The reasons you think of for him, such as having more things to do, taking care of the elderly is more difficult, etc., are not really reasons. You are just trying to convince yourself. The crux is in his heart, no matter how much you explain, it will be useless. The more you explain, the more doubtful he becomes. Can you have a long talk with him? Talk calmly and ask him if he loves you and what he is worried about. Your feelings for him are enough to reassure him. If he is making trouble unreasonably, he is forcing the marriage to a dead end and other things...if he still can't do it at all. Communication, then I can only say that judging from his current inner state, he will not be able to handle this matter and will always be between you two, seriously affecting the quality of your marriage. The outlook may not be optimistic, so you have to be mentally prepared...