@ggggrace I'm so sorry that you are struggling so much with this aspect of most - if not all - of heterosexual men's fantasies, and therefore with your DXPartners addiction to it. It is definitely an addiction if they have to look at, or watch, porn before they can get an erection. His addiction probably started when he was about 14 years old, so has nothing to do with how sexy and beautiful he finds you.
Mumsnetters tend not to read my posts, probably because they are usually very long - I like to explain things properly, and I also have what many people would think of as strange thoughts and/or outlooks on quite a few subjects. But if any of them are reading this (apart from 2 or 3 PPs) then I may give them the rage, but that is not my intention!
Anyway, it is almost 100 per cent certain that every single Mumsnetter on here who believes that their partner doesn't at least fantasise about other women -maybe someone in their office, or women they pass in the street, or the woman in a coffee shop that they noticed when they were in there earlier - while they are masturbating, or even while having sex with them, their much loved partner, is sadly very mistaken.
The difference is that most men do not tell their sexual partners about this. If asked, they probably very sincerely sounding, say something like "of course not, just because I am a man does not mean that I agree with objectifying women, or that I can't control myself if I see a woman obviously dressed to impress (and turn on). It is only ever you my darling who turns me on, you fill my every sexual fantasy; when I came home and found you in your pale gray joggers last night - you know the ones that poor little Jonny projectile vomited on that time - and found you on the floor fighting with the vacuum cleaner and something that seemed to be clogging it up, then it suddenly spewed up lots of dirty fluffy mess all over you, well I don't think I have ever fancied you more, which is why we had that marathon session a bit later, and I asked you not to shower first as I couldn't wait to get inside you..."
I must make a confession here, the rest of that mega sentence from after the semi-colon, probably/hopefully wouldn't have been said, or even thought about 🤞🤮
It all boils down to biology really OP.
Most heterosexual men (and maybe gay men too, unfortunately they are not part of my research at the present moment, but it does interest me, so I might be able to extend to include them in the future) are hard wired to reproduce. Those men of slighter lesser knowledge, or intelligence, might not realise this fundamental fact. However, it is already well documented that that fact is true.
How that fact actually translates into the behaviour of the opposite sex is not quite as simple as my last paragraph above might suggest, but it is also not a million miles away from it either. If we go back to cave men days, the men were probably all most attracted to the women with the biggest hips, the biggest bottom, the biggest breasts, as all of those things will have signified to them - rightly or wrongly - and maybe unconsciously, that those women would 'make' the healthiest, and most easily birthed children, and would therefore, probably be able to have the most babies. However, as civilisation progressed - if indeed it did progress 🤔 - and as knowledge and intelligence, and intellect grew, a great many men learned/understood that although a lot of them were still drawn to those more obvious "attributes", they realised that sometimes a woman with a slightly more slender, but strong and more flexible body, and with a thoughtful and intelligent brain, might actually bring healthier and more intelligent babies into this world, than their long ago ancestors did.
Of course, a large part of the occurance of much more healthy mothers and babies - in the West in particular - is not only down to better education, but - maybe mainly - down to the much better health and medical care that the mothers and their babies, and to a certain extent, the fathers too (their sperm needs to be healthy and mobile, and to be produced in significant quantities, to win a successful, very fast race) received both before, and during that stage of reproduction.
So, the point I seem to be struggling to make (in my defence it has gone one in the morning, and I have been typing this for a long time now 🤭) @ggggrace is that since the dawn of time, or at least since the emergence of both men and women, men have naturally been attracted to a wide variety of women, in order to try to impregnate as many as possible, so that they have the best chance to successfully produce little mini 'them'! Unfortunately, I don't think that the male psyche has ever lost that biological urge to keep on searching for the best woman to have babies with, even when they know intellectually that the woman they have at home is exactly the right one for them. All the being attracted to a relatively large choice of women to have sex with, is probably completely instinctive, and not one that they even realise the prehistoric portions of their brains are doing!
I think that the main problem with your still - at the moment - DeX, is why does he keep on being honest with you about his looking at porn and lusting over "real" women. Why doesn't he lie about it, like the vast majority of men do to their partners, unless they know that their partners are fine about it, and maybe even like to join in? Is it because one of his personal moral codes is that people, or at least romantic partners, should always be honest with each other, or do you think that he actually enjoys having enough power over you to make you upset?
I presume you believe his reasons for being honest are good ones OP? I can't judge that, and I don't suppose many people can, but I do know that I have rarely, but have occassionally told, what some people would call, "white" lies. My opinion, and my hope, about whether your beloved is honest with you for genuinely good reasons or not, is that from what you have said about his other behaviours, eg him being a great Dad - and yes he can be, even if he does get turned on by other women - and a lovely partner in every other way, is that he probably is, so I do think that he is actually, one of the good guys.
However, I don't think it is possible to change his basic sexual instincts, so if you do still love him enough to want to have a life with him, then I think you both need to go to couples counselling, and you will probably need to learn to accept him as he is, and to not cross question him about his fantasies, and indeed whether he still has them/looks at porn, and he needs to learn that to show you both love and respect you, that he must not blatantly watch porn in front of you, and to not openly ogle other women, which is actually usually horrible for the woman being stared at too! Also, he must not tell you about any of his fantasies, even if that means him lying to you about them.
Some people enjoy telling each other about their fantasies, but if that upsets one of them, then it needs to be off the table, even if that does mean lying to their partner concerning that articular subject. If you can't come to a joint agreement with him, that you feel reasonably happy with, then even though you have a little baby, and presumably a son who loves his step-dad, then I'm sorry but I think you will need to walk away. Please remember though OP, that if you meet someone else, he might not be addicted to porn, but he will almost certainly watch it, and/or fantasise about women in real life while having sex with you. The difference is that he will be lying to you...
I really hope that if you have had the stamina and patience to read all of this, that you don't feel I am being too harsh on you, I am genuinely trying to be helpful. I wish you and your children the happiest of futures, whatever you decide should happen with this relationship xx