I am a woman who watches porn and I can tell you that, from my experience at least, I don't watch it because I am missing something in my relationship. In fact I am perfectly satisfied and when with him, I also want to keep him satisfied.
Anyway, men and woman (for the most part) are wired up differently when it comes to arousal and sex. Its in our biology. Now just assume everything I am about to say starts with the words "Most" or "in general" because there are many exceptions to every "rule" but it saves me typing those words out each time I refer to "men and women"
Women tend to get more turned on with more of an emotional connection, whereas men are more visual. That's not to say men don't have an emotional involvement, they do of course, but men are often more turned on by visuals and it is often why they report some of their favourite positions as being ones where they can look down and see your bottom, or see the penetration, or see your breasts bounce and wobble. They are totally into watching our nipples harden or our orgasm faces and many other visual things. Now, it is a lot rarer that I hear a woman say "God, you know what REALLY turns me on? Watching his balls swing while we have sex"
Women on the other hand, tend to be masters of the imagination. Drifting away fantasising in our heads, thinking about that favourite fantasy, or imagining a time when we were with our partners that really turned us on and even elaborating on that and turning it into our fantasy sex.
Most of my exes and my current partner have admitted to watching porn and masturbating (I say admitted like its a negative thing, but thats how it seemed, almost like they were nervous to say they did) but being visual creatures it is harder for them to go into their head and bring back a faded memory. This is what porn is, its easy. Its like women thinking of their "Never fails me" fantasy or grabbing a vibrator, its easier. Watching porn for men is kinda like grabbing a microwave meal, its easy and will do the job of sating that hunger, but in reality men would much rather have that steak dinner, with all the trimmings. That doesn't mean that now and again, they don't just fancy a quick and easy microwave meal, because variety is the spice of life.
Porn is a masturbatory tool. It is not really that much different than a sex toy, in that its main job is to get the user from A to orgasm, after which, it gets switched off (just like a sex toy) and never thought of again until the next time the urge pops up.
You are not the only person who is threatened by porn. It is reasonaby common for some people to feel threatened by things that help their partner reach orgasm, or get aroused, without them. Sex toys and vibrators can have this effect on some males and porn has this effect on some woman, but porn, or sex toys are not a threat to your relationship and certainly do not represent how you feel about your partner.
I like to think of it this way: trying to censor your partners viewing of porn, or telling your woman that she is not "allowed" to own a sex toy, is trying to censor a basic urge that we all have. In my view it is the equivilent of telling a woman she is not allowed to fantasise about any other person, or sexy scenario that they have not already done together as lovers. It's like someone telling your partner they can never think about XYZ in a fantasy because you feel threatened by it.
It is trying to diminish the threat felt by the sex toy, porn or fantasy because WE feel insecure about what that means. Does it mean we are not good enough? Does it mean we cannot make them orgasm and they need all these "tools" to help?
It doesn't mean any of that though and it is certainly not cheating. Heck if thinking or watching was considered cheating, 99.9% of us would be guilty of it.
This is who we are as human beings. We have the luxury of imagination and we all use it. We also have basic urges and we have all been satisfying them since forever. I can imagine your husband masturbated long before he met you and likewise, you did too. This is a natural urge but sometimes we need a little something something to spark our imaginations, to get us from A to O and this is where toys/porn/fantasising comes in.
Actually, a surprising amount of people still masturbate when together with a partner. Even when happy with a partner, even when completely satisfied with a partner and masturbating does not indicate a lack of interest in your partner. My partner and I have sex about 4 or 5 times a week and I have the higher sex drive. I still masturbate, for the following reasons:
1) He isn't available. Maybe is is away, or busy, or sick, or not in the mood. Whatever the reason, I feel aroused and want an orgasm. I don't think any less of him and would, on these occasions prefer sex with him, but it isnt on the table
2) I just want to do it alone. The reasons have nothing to do with him. He turns me on like crazy and I love him to bits, but sometimes I don't want a sex session. Sometimes I want to chill out, lie back in the bath, close my eyes and relax on my own. I can't explain why, but what i do know is that it has nothing to do with him, his skills, his sexiness or anything like that. I just want to do it alone. The urge is there and I don't want to have a big, full on session. maybe there is no time, or privacy to have a full on session with him. So a quick, alone time session is like a stress reliever of sorts.
I would not give up my masturbation. I can tell you why...I like the variety. Again it has nothing to do with "Oh he doesn't satisfy me" and more to do with the enjoyment of variety. In the bedroom together, we use hands, mouths and genitals, we use words and touches...and all of this is variety, but so is masturbating alone and sometimes I want that option. for no other reason than I haven't done it for a while and the idea of doing it turns me on. Just like if you never ever gave each other oral, eventually it would be missed. The tools I use while masturbating (Porn/Sex toys/fantasies) are just that, tools to help me along. Sometimes I am horny but exhausted and just want a quick wank without the effort required for a sex session.
Have you even masturbated in front of each other? It is a very arousing thing to do together as a couple. I would honestly suggest you bring that into your sex life together, rather than seeing masturbation as a secretive, bad thing, celebrate it as another variety, more spice. Watching each other masturbate is extremely sexy, plus it gives you both pointers on how the other likes to touch themselves. It feels naughty too, which adds to the arousal.
Unless he is masturbating to the point where he would actively turn down sex with you, to go and wank in the bathroom, I can assure you wholeheartedly you have nothing...NOTHING to worry about with his habit and his reasons for doing it could include either feeling like he has the higher sex drive and is actually avoiding pestering you for sex all the time (Even though you are happy to have it) because he thinks you will start assuming all he wants is sex sex sex. Yeah, some men actually go masturbate out of fear of their lady assuming they are just after one thing. Secondly he could be in the common group of people who just occasionally enjoy a little solo time and I can assure you, it has nothing to do with you (Eg: He still loves you and finds you attractive and loves your sex life)
Sorry, this turned out long.
Good luck though and please, don't worry. Its only if he chooses his habit over you all the time that you need be concerned and just so you know, allowing him to indulge in his habit won't make him gradually enjoy doing that more and more and abandoning you...As humans, we love variety.