Excerpts of anything may be misleading.
Of course there is more to all of this.
(Rav Miller didn’t discuss abusive marriages much,but he did encourage husbands to buy conciliatory gifts for their wives)
Anyway: In the context of a husband who is treating a wife very decently, an unhappy wife MAY- not necessarily though- fit the above description.
But let no one jump to this conclusion about any wife seeking a divorce.