Ah the porn debacle. As April mentioned above, men are often stimulated sexually by things that are visual more so than women and porn is a medium that provides just that; however, many women enjoy porn as well (so it's not just a man's thing). There is nothing wrong with watching porn (unless it interferes with work, life, etc) although the conflict that it is causing in your marriage is the problem.
First, I want you to consider that, ever since your husband was young, he likely incorporated porn as a part of his sexual expression. More specifically, he likely always used porn for self-pleasure (masturbation), which means porn is part of his pattern. This is something he has used since he was young and, as much as you want him to, it's hard (and I'm sure unreasonable) for him to stop cold turkey. You asking him to and him not being able to stop isn't his attempt at pissing you off or ignoring what you say. Rather, it is one of his sexual outlets to use porn when he self-pleasures, both of which are a normal expressions of sexuality.
To address you mentioning that you feel inadequate and that you aren't enough for your husband. Are the two of you still sexual with each other? (if not as much as when you first met that's normal). Does he kiss you and tell you he loves you? Does he say how beautiful you are? Do you kiss him and tell him he's handsome? If no than I would be slightly concerned. If you answer yes, then I cannot see why him watching porn is demonstrative of you not being enough for him. Evidence of this is that you mention you found porn since the beginning of your relationship. So it isn't that he's just now really into porn because you aren't enough for him. He's watching porn because, well, that's just what he's been doing since he was young.
Further, because he most likely uses porn when he self-pleasures, are you comfortable with the fact that he self-pleasures? Try not to see either one as a threat to you or demonstrating that you aren't enough for him. Pleasure is a wonderful thing so try and allow your partner to experience it it many ways, as well as allow yourself to experience pleasure in many ways. Although it's difficult to understand that a partner has other means of sexual expression aside from when he is intimate with you, we are sexual beings and have many means with which to express it.
Overall, your partner watching porn or self-pleasuring is not something to worry about. And sexual desire/attraction isn't all in how much you have or haven't gained or whether or not your husband is into porn, it is YOUR confidence and YOUR acceptance of yourself that will help you to know you are one sexy woman.
If you have any question, feel free to send me a message on the site or e-mail me at drchelsea.co@gmail.com