Concerned about porn use

My husband has been looking at porn on the internet to what I consider to be excessive levels - he spends over $400/month on different memberships! What's worse is that he hides it from me and he knows how much it upsets me. I've told him it makes me feel like he would rather be with a picture or a video rather than me. Our sex life has suffered a great deal in this time frame. I think it is because he can only get turned on by porn.

This issue came up several years ago when he was out of work and we resolved it. It has since surfaced again under similar circumstances (he is out of work again), only this time we have been trying to have a baby without any luck for a long time. Now, I'm not even sure I want to/should have a baby with him or even stay married to him.

I'm sick to my stomach constantly agonizing over this. I can't understand why, if he loves me and respects me and knows that this bothers me so much (mostly because I think it impacts our own intimacy), why would he continue to do it?

Distraught,
I think that a little porn is ok and that a lot is very bad.
You said that you resolved this in the past...is the previous solution no longer usable?
My suggestion is to try to find out what the porn is giving him by asking him. Maybe he wants to do some "freaky" things and is afraid to ask you or reveal that different things turn him on.
Show him you are open to his sexual needs.
If that isn't it, I say do not have a child with him. Pornography promotes women as objects and not as human beings. It makes people care less about the emotional side of sexual relations. If he can't stop, he needs professional help for the sake of your marriage and his life.