My partner doesn't consider cybersex via a webcam to be cheating

My partner of three years has signed up to a porn site to engage in sexual activity over webcam. When I confronted him he said that most of the women weren't genuine, he was successful only once and had never considered it to be cheating. He claims I have no desire to engage in sexual activities he likes and that I don't provide oral sex often - I avoid it because sex is so rare I don't want to service him and go another five weeks without. I'm confused and embarrassed because I'm always trying to gauge his responses to my advances.
The availability of cybersex draws many people to what they think will be uncomplicated and exciting. But since there are diverse ways to view this kind of sexuality, it's always wise for partners to decide early on if it violates their exclusivity agreement.
People often wrongly assume their partner has the same views as they do, leading to the same feelings of betrayal that you're having now. Give him a free pass for his past cybersex exploration, then have a constructive discussion about the future.
Persevere in trying to understand his sexual responses and desires and come up with some ground rules, such as taking it in turns to initiate lovemaking. Most importantly, try to get the fun back, either by playing sexual games or experimenting with sex toys. You need to be creative in order to find a way out of this rut.

Source: https://www.guardian.co.uk/lifeandstyle/2013/apr/15/cybersex-webcam-cheating