TL;DR: 1) Looking at someone has nothing to do with wanting them.
2) There will always be someone prettier and sexier and the only thing you can be the best at is being you.
3) Only you can fix your insecurities, and you should do it soon before you drive people away.
Hey. I'm a girl and a couple of things may be helpful.
First, you're equating your BF looking at a girl to him wishing you were them. That's not how guys (or girls) work. First, looking happens. It's a near subconscious thing. Just because he notices women doesn't mean he desires women. He's with you for a reason.
Are you telling me that you've never looked at any guy ever since you've been with him? That all of the sudden guys became invisible to you? As far as "evening the playing field" goes, most (not all, but most) straight women enjoy non-nude male bodies more than nude ones. So yeah, in the summer when it's hot at the beach and guys are in tank tops with their arms, legs, abs, etc out, women notice. And guys notice that we notice. And it isn't a big deal because adults can appreciate eye candy while not losing any desire for our partners.
If/when he watches porn do you think that he wants those women more than you? Or that the simple arousal he feels watching it compares to what he feels for you at all? I hope not because that would be irrational for the same reasons.
The other thing you need to understand is that you'll never be the prettiest, smartest, most successful, funniest or sexiest person in the world. Or even in your city. There will always be someone more -est. Accept that. The only thing you can be better than anyone else is you. And fortunately, your bf chose you as the person he most wants to be with. Girls can have bigger tits or a better ass, but they wont ever be as you as you are. That's why your bf only glances at them in passing. Even though they may have a noteworthy rack, they aren't you, which is what he wants.
Ultimately, you have to be the one to make yourself feel better about this situation. He can't fix your insecurity. No one else can. Until you stop feeling that you aren't enough, no one can ever do enough to make you feel like you are.
To be honest, you need to work on this because you risk alienating people with your insecurity. Obviously he should be discreet and not blatant with whatever looking at women he's doing. You should know that it's a red flag when someone can't handle any perceived interaction with the opposite sex because it triggers your insecurity. It gets extremely tiring when you have to constantly reassure the person you are already with that you actually want to be with them and noone else. That should be pretty obvious, shouldn't it?
When you're insecurity makes you want them to change their normal behavior to make you feel better, there's a problem. I used to have insecurity issues a long time ago. The books The Four Agreements and He's Just Not That Into You helped me grow up and get over that. I recommend that you read those books and hope they help you, too.