My partner is having a foot fetish and he's done some bad stuff

I've been with my partner for nearly two years now and when we first got together I started noticing little things where he would be following accounts on social media to do with gymnastics and putting notes into his phone of instagram names to do with fitness and yoga or gymnastic profiles. I knew he had a foot fetish and he's done some pretty screwed up stuff. I caught him taking a picture on my cousins feet when he was asleep and he emailed the picture to himself so he could delete the picture from his camera roll. I confronted him about this and he said he didn't know why he did it. On other occasions I've caught him watching videos online with stuff about kids feet challenge or little boy feet, sleeping challenge, boy swimming, boy getting changed and many more stuff. I've recently found out that from the age of 14 he'd been google stuff about child pornography,boy getting raped, man kissing boy, boys anus and other weird stuff. I've told him loads of times it's not acceptable and I've threatened to break up with him over it and each time he's gone back on his word and gone and done it again. He's been doing it again recently Googling feet challenges on YouTube in the car before coming home from work and deleting his history but i had a massive serious chat with him about it all and he's promising that he won't do it again and that he doesn't want to be that person anymore....even more so now that we have a son! I've suggested to him that if he wants to look at boys feet or feels the need to YouTube something to ring me so I can talk to him and remind him that it's not acceptable to do so and to just kind of talk sense into him. He's been in the routine of googling that stuff since the age of 14 and he said that it's hard to get out of that routine but he keeps having these slip ups.....what else can I do other than try and help him? This is the final straw now because we're constantly arguing over it all and it's draining me, im constantly paranoid and checking his history on his phone or worrying if we go out and people have their feet out....it's a massive problem for me because like I say, I have given him so many chances for nearly two years now and every time he's said that he won't do it again and expressed that he doesn't want to be that person anymore and he's ashamed and embarrassed so I'm just thinking that this is no different to any other time, in a few weeks he'all have the thought of looking at kids feet or whatever and he'll do it & that's why this time I've suggested that he rings me or talks to me about it because I want to help him change....I've seen a massive improvement with him from when we first got together to now! It's just these slip ups he has. Any advice please? I would really appreciate it