If looking were hurtful, then I'd let him know. But it's not. It's really natural and normal, and not the first step to an affair, much like looking at a car isn't the first step to vehicular manslaughter. Looking and having sex are two totally different actions.
Really, if we were to judge and condemn all actions in our spouse that could lead to sinful behaviors, then we'd be doing nothing but criticizing and attacking our spouses for everything they do. This is where having trust in your spouse comes in. If you trust your spouse, you won't need to rebuke him for doing something wrong before he does it, even if it's not something he was going to do. If you don't trust your spouse, then sure, maybe it's appropriate to react to things that he could do, but isn't doing.
Is it gullible to take the word of your husband now? Again, I think it's more indicative of the state of the marriage than the tresspass of looking when we are to assume that the word of our husbands are false, and that to believe them and trust them makes us gullible. If my husband says he's looking because of how a woman does her hair (especially when he knows looking doesn't bother me, thus he has nothing to gain by lying), I trust him enough to assume that's what he's doing, instead of convicting him of the sin of adultery (before he committs it) and lying (even though there's no reason to suspect he is).
When we're out to purge sin, we have to make sure that what the people we're accusing of sin are actually proven to be sinning first. It doesn't make for a good marital relationship when we think the worst of our spouse, react to tresspasses they haven't done but assume they're going to do the worst.
We're each accountable for our own actions, you're not responsible for his. If he chose to do these things, it's not because you allowed it, but because he wanted to. Here's guessing that he knew those things were wrong, as most people know that sex chats and such are inappropriate when you're married, but he chose to do them anyway and he would have done so even if you had harranged him unendingly about what he did and didn't do that bothered you.
My husband knows looking is looking, and having sex is having sex. He knows that looking doesn't mean it's OK to have sex with who he's looking at, or that I condone his having sex chats or roleplaying with other women. If he were to use the excuse "You were OK with looking, so obviously that means you're OK with me having sex" then really, he's trying to fobb off accountability for his actions and lay the blame and fault on me... When the issue is his boundary issues, not mine.
Well, I find it disheartening that people would seek to apply unrealistic standards with severe punishments to their spouses for behaviors that are not only natural, but only harmful due to the personal issues of the person who's offended. But, as you said, that just shows us that the Lord has layed out for us.
I don't think there's anything wrong with expecting to be the only person your husband desires... But only looks at? That is unreasonable. Unless we expect and want full mental control over our spouses, and wish to dominate their free will, it's just not reasonable to expect that they will notice and find attractive nobody but you.
Just the opposite, actually. I don't care because the other person poses no threat. My marriage and relationship with my husband and the trust we have with eachother is not so weak and flimsy that the mere sight of another attractive person can undermine it. Our marriage is strong and healthy, so while some marriages may be of a state where seeing another person undermines love and trust, ours is not. The pledge my husband made to me is worth something, it has value, weight and merit, and can't be undone simply because a person who's in his life for less than 30 seconds and never has direct communication who looks attractive.
So another girl is cute. Who cares? Is he going home with her? Nope. Is he having kids with her? Nope. Did he pledge to her before God and our friends and family that he would be with her for thick and thin for the rest of his life? Nope. So what I have on her is so much stronger and better than what she has simply by being attractive. So he can look all he wants, but in the end, I'm still so much better than the girl he's looking at, and our marriage is so much stronger than to be crumbled by the sight of a pretty face.
I'd like to point out, if the behavior makes me "cool" with my husband or his friends, that's not the point, but it is something to think about. If my husband feels that this behavior makes me easier to be with, more approachable, and more supportive and understanding of him, is that a bad thing? If he knows honesty won't make me flip out and punish him, he's more inclined to be honest, and he's not going to feel pressured into lying. Thus when he sees a girl with interesting hair, he can comment "I looked at her because of her hair" instead of having to yell loudly like a paranoid person "NOTHING! I WAS LOOKING AT NOTHING!" and think that I'm now going to be unduly injured or offended because he had the nerve to notice another person.
I don't care to be cool either, but I do care to be the type of wife who displays trust and respect for my husband. And having been out with the spouses of husbands who freak out when their husband so much as looks at the waitress too long... Yikes. That behavior makes everybody, spouse and friends, miserable.
I'd rather be the wife who's a good catch, who's fun to be with, who's rational and reasonable and thus is invited out with her husband for all sorts of amusements, who's friends with her husband's friends (and thus supportive of his external relationships and endevors), than the harpy married to a buddy who you never want to see or go out with because her poor behavior and over-reactions make being with them a nightmare, and it means that every little thing you do must be done while walking on eggshells for fear of irritating her and causing problems in their already fragile marriage. Then, not only is the trust in their marriage destroyed, the value of their vows destroyed, the dynamic as a husband and wife destroyed, but now even friends want nothing to do with us because we're such a disaster to be with.
That's not what I want.
And ask yourself this... By demanding your husband find nobody else attractive and have eyes only for you, is your marriage in a better space? Do you feel more loved? Or do you and your husband feel closer together, or more divided than ever? And why are you allowed to notice an attractive woman, but he is punished for noticing same attractive woman?