My husband has left me four times for other woman. He is always falling in love, yet he says he loves me. What is wrong with him?
What is wrong is that he has learned he can have his cake and eat it too. He can go off with other women, and knows he can always come back to you. Likely he is somewhat immature, and needs his ego stroked. Once the excitement of the new romance wears off, he is back where he started.
If he is back with you now, you need to tell him it is the last time you will take him back, and mean it.
If he is with another woman, it is time to file for divorce and get on with your life. A man who has left you four times does not have much commitment to your relationship, and you can never be sure when it will happen again. That is no way to live.