My boyfriend denies his problems with porn. What determines an addiction

My boyfriend of 12 years has what I think is an addiction to porn. We have been together for 12 years.  He says he?s been watching porn at least 2-3 times a week for his entire adult life.  He is now 41.  Our sex life has completely stopped.  We had multiple discussions about his porn use.  He denies he has a problem.  He says he can stop.  He says it?s because of me why we don?t have sex anymore.  Says it has nothing to do with porn.  Says he still loves me. 

He is open ( at times) to seeing a sex therapist.  But then he backs off.

My question is :

What are the factors that determine he may be addicted to porn use?  He has all of the physiological symptoms.  Can?t stay erect during intercourse.  Has no libido ( for me anyway).  Cannot ejaculate with me any longer.  Etc. 

Thank you. 
My mental health is being destroyed through all of this.  He says some very hurtful things to me regarding this.

Hi there. I am so for all of the hurt you are experiencing. This situation is never easy and I understand the feeling that can come up. Know you are not alone in this. What you describe does sound a lot like a porn addiction and maybe even PIED but I am not a professional. A reboot wouldn't hurt anything. The most important thing is communication though. You two need to be able to talk to each other and share your thoughts and feelings freely. If you can't do that than porn addiction or not you have some real things to work out. I know this can feel overwhelming and you go though a see of emotions, it really does just plain suck. At the end of the day there is support here. You are welcome to ask questions, seek support, and be able to vent frustrations whenever needed. Welcome. While I am sorry for the situation I am glad you found this space.

Our mental health does go down the tubes, no denying that!  A lot of men here choose to not let partners know, but that is important.  Then we can talk and help with solutions.  Boundaries are so important during this time.  Don?t ask him if he uses.  Tell him you know he is using and the signs you see and how it affects you.  Tell him what you need from him.  Then see how it works.