It gets me off.

I don't think watching porn is cheating.
However, I think you should probably work on your physical relationship with your wife. It's really easy to lose your physical relationship with someone after a lot less than 20 years.
There must be a wealth of information on this online and there's no shame in going to couple's therapy.
What would be a gigantic mistake is thinking things will be better with another woman. After the first time or two, your guilt or fear of discovery will probably overshadow any pleasure you might have. Is that worth destroying a 20 year relationship which seems pretty good? After all, you are asking if porn is cheating, so you must still care for this woman.
Get to work pal, and rekindle the flame that has dimmed on your bedroom. You can do it.

You actually consider leaving your wife for porn?

...That's a good idea.

She might approve if she knew that's why she's getting good sex.

I assume you've checked out her views on porn? Has she ever seen any?

I don't think it's cheating in the traditional sense, but dishonest in that you're keeping something important to you both a secret from her. However, I can see why you'd be reluctant to tell her if she's totally anti-porn.

What about mainstream stuff in movies? Is she ok with that? Sometimes it's the idea people of internet porn that's the issue, although I personally find most of it silly, repulsive, degrading or just plain boring.

I guess you need to decide what you want to lose: the good sex or the porn? I'm not in favour of dishonesty in relationships (partly because I'm very bad at it!) BUT sometimes total honesty can be dangerous.

In my opinion most men don't really have erectile dysfunction, they are just bored with their wives and are no longer turned on. Watching porn actually makes this worse, like Viagra, the more you use it = the more you need it.