Dora,
You have a decision to make. If you choose to go down this road, know that it is a hard one. You have to read the information. His addiction is in his brain. If you haven't already, watch the videos, read the science. Yourbrainonporn.com is one that I highly recommend and most people are using to learn about this.
First off, it's not your fault. It's not your relationship's fault, even if it is long distance. If he has an addiction, he will have to seek help on his own. Not just trying to stop, but joining the forum, going to meetings, getting a therapist, having an accountability partner and working a program. It's not easy work and it will be hard to convince him as he may not be ready to accept this. You can help him by sharing the information with him, getting him to realize what he is doing to himself and also helping him to realize what it does to you can help sometimes. But ultimately you cannot make him, and it can be the hardest truth.
Addicts are more attached to their addiction than you. And their brains will get them to lie to you. They will get them to do things they wouldn't usually do.
You're brain is also going to go through changes after knowing this. I'm so sorry for all the pain you must be feeling, all the other significant others here know exactly what you're going through, starting here is a good place. There are others who have more information on how you can find peace and help for yourself. Remember to stay calm, take care of yourself and know that you cannot control everything, you are what is important.
Stay strong, dear, and keep reaching out. There is also http://www.pornaddictioninfo.com/boards/index.php where I also post. We don't have to go through this alone.