If you feel like it is cheating, then yes, it is cheating. The energy from the marriage is going elsewhere, and that is why, in most cases, it feels like cheating.
In order for anyone to overcome an addiction, the internal cause must be found. For my husband, it was lack of connection during childhood that caused him to turn to that stuff. The dopamine rush and accumulation of DeltaFosB from it that he felt is what eventually created the addiction. This then prevented him from having a real connection to someone who was not on the screen despite his want to do so.
My thoughts on this in general are that, if someone turns to something that could potentially be addicting, it is because they feel as though something is lacking in their lives. This is an internal factor that has not been addressed, usually due to the individual being unaware of an issue to begin with. To place blame on someone else is just wrong. You could be the most loving, supportive person in the world, but if your partner has issues, it wouldn't matter. They would still seek out ways to escape their internal struggle.
I think what someone on this thread was trying to prove was that, if you, as a partner are not fulfilling your part in a marriage or relationship, your partner is then going to find a way to fulfill their needs elsewhere, and you should reflect back on yourself on what you did wrong. This is not true. Someone who doesn't feel as though their needs are being met in some form is having an issue within themselves. It is not the responsibility of others to make up for what someone else feels they lack, even if that person is your SO. The one who feels they need to look elsewhere to make up for what they lack will never be fulfilled on the level they need. This is an internal issue, and no amount of excuses will ever make it okay to seek elsewhere.
I strongly believe that the opposite of addiction is connection. There are many studies out there that prove that people who avoid the internet are happier than those who spend a great deal of time on it. You can't connect to a screen, no matter how hard you try.