As the wife of a PA, here is my opinion:
An addiction is when a person becomes dependent on a substance, thing, or activity. An addict compulsively rewards themselves with something despite the consequences; in this case, P/M/O. The addicts brain becomes addicted to the neurotransmitters released in the brain during arousal.
To me, a PA DOES physically cheat. P addiction isn't "just" mental infidelity. When you are a PA, your addiction is usually accompanied by physical acts (whether you agree or not). Anytime the PA was having sex w/ his SO, he was recalling the images of women/men during sex with their partner. The PA literally visualized & fantasized that their SO was someone else. Again, to me, that is physically cheating (he might has well have, right?)
P addictions take work & time. P addiction never goes away; it's something you & your partner will be working on for the rest of your lives. When a person has been a PA for a long time, they have put the time & effort that should have been spent in their marriage, into P instead. For the duration of your marriage, the PA has chosen to lie. My PA husband admitted to PMOing *at least* 2x a day, most days. We've been together for 10 years. This means, my husband chose to PMO to other women approximately 7,300 times in our relationship. This doesn't include all of the times he's fantasized about P during our "intimate" moments .
I feel revenge physical infidelity because you married a PA makes you no better than the addict; morals, ya know? However, I do think revenge infidelity would & should be easier to handle in the marriage. A physical affair (especially a 1 night stand), is a single event that could be summed up as a simple "mistake". It would be done, over, & the SO would be remorseful. The physical affair would be based on emotions only; it would hurt the marriage, for sure, but I think it would be easier to overcome vs PA....