There are only so many reasons why someone wouldn't work. Either to stay home with children, because they're not physically or mentally capable of working, or because they just don't feel like it. Being unemployed because of inability to find work is also a legitimate reason but one would not expect that situation to last 18 years unless he wasn't *really* looking all that hard. Someone without minor children who is physically/mentally capable of working but stays home "to keep the house" or other such nonsense I would put in the category of "they just don't feel like working". Or someone could choose not to work in order to go to school, but again that doesn't appear to be the case here and should not last 18 years unless you're staying in school as an excuse to not get a job. All of the above are valid choices which may be acceptable choices for any given family. Some reasons may be considered to have more weight than others by a judge when deciding about spousal support, but that's not my place to say.
It doesn't really matter what I would find acceptable in my family. For me to support a non-working spouse for that long, there would have to be some serious extenuating circumstances or he would have to be the most stunning example of a house-husband that one could ever wish for (in which case why would I be divorcing him), but that's me. OP decided it was ok with her to do so, and that's the circumstances that the judge will rule on.