Me and my fiancehave been together for 4 years, and about evry 4-6 months i catch him looking at porn and it i?

it makes me sick. ive explained how it makes me feel like im not enough for him, we have two kids age 3 and 1, so its not like we get to do it 3 times a day like we use to, it more like 2 or 3x a week and were adventurous and its amazing when we do, and maybe my body isnt as nice use to be but ive lost my baby weight. but itsnot fair to me, that im left with nothing while he wacks off to sluts! when we first moved in together he would buy it on our tv and lie that he didnt do it and i was dumb enough to believe him, until i found a magazine. now he admits to it when i find it on the comp and he doesnt understand why i care, ive left him for a week 2x trying to make him realize that im serious that if he doesnt stop i cant be with him. i cant even look at him when he does this. ive tried to make myself not care about it (that its just somethin guys do, and atleast hes not screwin some other girl) i know people deal with alot worse with men, but i just cant get over it. i love him and want to spend the rest of my life with him and he get really upset when this happens but its his own fault. i gave him the ultimatum its porn or ur family. pick. about 6 month ago and i just caught him again. im onthe comp about evryday and he doesnt know how to erase the history so i know when he does it. and we have regular tv now so he cant buy it. why does he do this?