"Aaron could find some emotional relief because he caught sight of the anger and resentment he had so long been denying. Once he had this knowledge, the question of whether his anger was justified fell away; no longer bearing down on him in secret, its force simply faded."
So Aaron briefly realizes his own resentment and anger toward his musician husband's lifestyle. Then can't he be even more angry about it?
Aaron had some deep-down, partially-formed belief that he worked harder than his partner Jim, without even knowing it. That subconscious belief led him to be passively aggessive.
By acknowledging that belief and the associated anger, he can now look at the belief logically and solve it. Does Aaron truly believe that he is a harder worker than Jim, and is that a problem? If so, he should talk to Jim about taking on a side job or more chores, or maybe break up with him. If not, then he should consider what might be fueling that belief. For example, Jim might work his ass off practicing and performing and cooking good food, and perhaps Aaron could do more to appreciate that.
Disclosure, I guess maybe I'm more of the "openly hostile"/IDGAF camp like some of the other commenters have expressed, so I find it harder to imagine Aaron's position where they are not even in touch/aware with their inner feelings of anger and resentment about something. Then again the author says everyone is susceptible to being passive aggressive.