Husband and lover have been together for six years, and basically go to her place once a month, but what's the point of calling that woman every time she drinks?

Your husband may get emotional when he drinks, so he needs to drown his sorrows or seek comfort. He may feel that he can get some comfort with his lover, or meet some psychological needs, such as being cared for and encouraged by the other person and feeling needed and loved. This behavior may show that he is highly dependent on his lover, but it also shows that he is dissatisfied or lost with the marriage relationship. I suggest you communicate frankly with your husband, seek professional help, find out the root of the problem and solve it together.