@LillyBird Welcome to TAM!
There's a couple of things to unpack here so bear with me.
First this: "He is mostly an honest person"
That's a problem. I understand minimizing something that will hurt your partner, but for you to be secure in your relationship you need to know that he is honest with you, in spite of any pain it may cause. In my mind, this is the biggest problem I see in your OP.
Next, about porn. Feelings across the world and here on TAM widely vary. The biggest thing I can tell you is that whatever boundary you have regarding porn needs to be communicated to your spouse and respected by your spouse. But there's no right or wrong answer. Some men or women consider viewing porn the same as infidelity while others are not bothered at all. Pick your own path, be comfortable with it, and then discuss it with your spouse.
About this: "By the way, do men do this?"
Men (I am one) widely vary in what their imaginations allow. For the most part, I do not think it's like that, and certainly, it's not like that for everyone. Some maybe.
I hope this helps. Your concerns look perfectly normal to me and the fact that your (husband? partner?) may not be respecting your wishes is troubling. You and he should discuss this openly and involve a couples counselor if you can't find agreement on the issue. But if he is only "mostly honest" then any agreement you have is going to be hard to trust.
Best wishes to you.