Here basically you are asking whether Zina or treating husband badly is worse sin. I think zina is worse because in addition to being a great sin, it has lot of worldly problems which can be difficult to solve. For example, if husband came to know this it can lead to divorce or it can lead to illegitimate child. So the problem of zina is not limited between husband and wife, it can have far reaching consequences.
In the case of woman who treat her husband badly or neglect him, it can be solved through family counselling or sometimes the problems between them may resolve on its own after some time and she may start to treat husband nicely.