Is watching porn considered cheating while in a relationship?

Kayli
I found that if i spend one night without my boyfriend his first go to is porn. I feel really uncomfortable with the whole porn thing. I tried talking to him about it but it just started a fight. We have a healthy no secret relationship. We have sex, a lot, and we have a pretty open relationship when it comes to sex. 
Can I get other people's opionions when it comes to porn while in a relationship? 
Is it cheating or not? 
What should I do..