I can certainly appreciate how you might feel now: betrayed, lied to, cheated on. Your s.o. has been jerking you around for a long time and you would like to say or do just about anything to get him back. Throwing the damnation card would be wonderful and gratifying, and my gut reaction would be to say that this is absolutely infidelity. However, the Torah would seem not to share this sentiment, at least from a legalistic standpoint.
Infidelity in Jewish terms only applies to one type of relationship: marriage. Biblical marriage actually has two stages, kiddushin (betrothal) and nissuin (full marriage), but the ceremonies are now done back-to-back so for our purposes only a married couple can cheat on each other. Furthermore, the only type of act that has actual real halachic (legal) significance that in fact divorce would be required would be actual sexual intercourse, defined as regular sexual intercourse and “unnatural” sex. Voyeurism in strict legal terms isn’t anything since the person didn’t do a physical action. The Talmud in Shevuot points out the fact that a person being required to bring a sacrifice for taking a false oath is already a novel concept since all the person did was say something without doing a physical action. Watching something isn’t doing anything, and many a waist line can attest to this.
This does not take away at all from the fact that your partner has severely violated your trust and has violated a Biblical prohibition besides for obviously surfing porn which is a form of entertainment completely antithetical to everything we stand for as Jews. He is guilty, apparently repeatedly, of taking false oaths, that he will not do such-and-such. Swearing falsely is in the Big 10 that he should be familiar with. He is also guilty of acting deceitfully and not distancing himself to falsehood. Claiming that he is a porn addict is a lie and a sorry excuse. You’d know if he was really a sex addict because he wouldn’t be able to hold down a job, would have hygiene issues, or have some other issue with normal functioning. The only problem he seems to be happening is keeping his word to you.
I say this with one caveat: if you did know about this or any issue at the beginning of the relationship and continued to pursue it anyway, it might be considered a stamp of approval of sorts. In the formal marriage institution, if there is something about the woman that had the man known about he would have never affected the marriage transaction, the marriage is annulled retroactively. However, if after they are married he continues to stay with her, it is considered as if he “forgave” the condition and he accepts her as is. Then the marriage is fully in force even if he decides to complain about it later on.
I do want to revisit one point because I believe I would be delinquent as a rabbi not to expand upon this thought. As I said earlier, infidelity only involves married couples. According to Jewish law, a person who didn’t put a ring on it isn’t cheating in the literal sense if they decide to go outside the relationship. Technically they are still shopping, and my experience with this generation is that unless someone is at least engaged they are in fact really still shopping. Six years later and he hasn’t proposed? It doesn’t take six years to know someone well enough to know whether or not you can spend rest of your life with them. This person may already have one foot out the door, and the porn is simply symptomatic of that. The fact that he won’t stop after six years fully knowing how much this upsets you is ahzariut (cruelty), plain and simple. You don’t treat the people you love that way. The big problem of course in our generation is that people do treat the people they love that way. That doesn’t mean you have to tolerate it.