They say men are kind of hard-wired to not be monogamous (evolutionarily). It's definitely normal to be intrigued by other women (and to have a desired to mate/bone/do the horizontal mambo with them). But if you're not happy with your relationship then that's different I guess. But I would definitely say it's normal and not an addiction unless you are super-obsessed with porn or fantasizing or something, which is also relatively "normal" but maybe something you need to deal with by taking some sort of action like therapy.

Men are supposed to have a drive to want to to sleep with women they find attractive - that's millions of years of evolution telling us to spread our seed and pass on our genes as much as possible.