Mental / emotional infidelity is still infidelity.
One can debate the practicality or validity of exclusive relationships but if that's what you've agreed to then that is the agreement you must honor. If you aren't getting your needs met through that agreement then at least have the integrity to say so and remove yourself.
But I don't think that's it for a lot of cheaters ... I think they want the security of a stable relationship AND the intrigue and fun of an illicit one. And that is dishonest.
Sexting yes but texting no.....perhaps distant chatting is trial balloons b4 asking or answering with our local love....I never SEXT even faithfully to my only partner ....love is only joined air shared water planted soil stars gazed only together not triangulated by cyber electrons