Flirting is flirting. £@%^ing is £@%^ing. Porn (from piccies to live naked ladies or men dancing for your enjoyment) is porn. Three different things, whether they are IRL, on the 'phone or online.
£@%^ing someone else is cheating, unless you have an open relationship. By £@%^ing I mean sexual activity, as in activity that is sexual. Doh. I do think there is a difference between doing it online and IRL; Lilac, you say your friend is just as hurt... nah... I think she'd be even MORE hurt if it was IRL.
Flirting may make your partner angry or sad because of their insecurity, or may be taken so far by you that it would make the most relaxed person annoyed. There's innocent flirtation "Heya sexy legs, you look great in that" "No, your tits are fine, don't get a breast job", etc., and there is flirting with intent. Innocent flirtation is or should be fine. Flirting with intent is nasty.
Porn... well, it really bothers some people. I think people who object to their partner ever looking at porn 'because why should they do that when they have me at home' should just get over themselves. Obviously if it's a question of never being able to use the PC because it's sticky and surrounded by tissues, then ball busting is reasonable. But some porn here and there? God, rather that than sport or war movies.
Butalbee, I don't think you're a sex addict, I just think you need £@%^ing. Completely natural. If you were a sex addict, then you'd be getting £@%^ed, as that's what addicts do. Calling you a sex addict is like telling someone who talks about drugs a lot a drug addict. Hmmmm. Non sequiter.
Just because someone is horny and likes talking about sex, and because they are horney lust after the last bit of action they saw does not make them a sex addict. I hope you find a nice bloke or blokette to move your world.