Why am i not enough for him?

My husband used to have a girl that he talked with when we both havent dated yet. Weve been married for 5 yrs now, and he still mention about her that he wishes he chose her instead of me. He also talks about his ex wife, about how shes better than i am. He says im a bad wife, and every one else is better than i am. But when im gonna leave him, he says the opposite, that im his number 1. Idk how much i mean to him, i mean a lot to him. Im his world, but when im back to him, he goes back to saying im a bad wife, his ex are better than i am. He wishes he couldve dated those other women instead of me. Its like a cycle. Why is he like this to me? I gave him 3 kids.