ok this was requested by LeaderOfFeeless
but I agree
First of all, RPs are done with characters, either ones made by yourself or canon characters from games, shows, etc. so you aren't even rp-ing from your own viewpoint you're doing it from the viewpoint of those characters,
second of all characters are fake, 100 percent fictional, so even if you were using a self insert or, just rp-ing as yourself with that character it's not cheating because half the party is non existent XD
really the only way i would consider it cheating is if you were rp-ing, as yourself, with another person, who's rp-ing as himself (or herself or themselves) and doing sexual or romantic shit when you're already in a committed relationship AND your significant other is closed off to the idea of you looking at or being with anyone else (i'm saying this because some people are in polygamous/polyamorous and open ended relationships also so this is more or less for people -not- in those situations trying to judge them based on their own standards)
but yeah, no, NSFW rps aren't cheating- if you feel like it is you're just insecure about your relationship or yourself.