I agree with Victoria and the other posters who said it's just FANTASY. Not real.
Could you compromise and see what excites him. I personally see no harm in porn, for either a man or woman UNLESS it overtakes real life. I as a woman, enjoy porn, all sorts even lesbian porn but I am definately straight.
I love my man looking at porn, am I in the minority here, odd ?
We look at porn together, he shows me what he likes and we both get hugely turned on, and swap fantasies. To see him appreciating the female form is exciting, I encourage him to tell me what he'd do even, in the various situations because it's NOT REAL.
We fantasise of 3somes etc but again, they are just that, fantasy. No way, in real life would a 3some happen or would he be encouraged to 'choose his favourite' from a group of women.

Your man is not deceiving you nor is he using you. Sure, the porn ignites his spark, but it's YOU who lights the fire. If you were second best, he'd be out looking for his thrills elsewhere. He wouldn't have sex with you if he didnt desire you.

Relax, compromise, agree how much sole porn time he has, and maybe have porn time together. Make it fun.

You might even get turned on by it yourself, afterall it's just fantasyland, and we all need to go there once in a while.

Try it, you may surprise yourself !

Good luck, enjoy !