Unfortunately the fetishes you mention happen to be the most popular ones out there and the porn industry knows it and feeds it as long as they can make a buck. What happens is guys masturbate to that kind of porn until they associate sexual pleasure with the fetishes they watch. I am from the pre internet age where you had to go out and find a girl to do those things.
I have done all of those things you mentioned and more over my 44 year marriage. I did not know what they were called but our friends asked to wife swap and other friends invited us into soft swinging. My wife is the one who asked two girlfriends to join us in bed and her best friend to have sex with me to cheer her up after a bitter divorce. I never went looking for these things. I have been on most of the major sex forums and see all the guys talking about the fetishes you mentioned and bemoaning the fact that their wives will not do it for them. There are several reasons for liking those fetishes that range from bisexual urges to wanting to see a live porn show and then go home with the star.
For most it is just masturbation fodder. My wife and I are very open about masturbation and what turns us on. She does not mind if I look at porn as long as she benefits from it.
I would not worry about it as your husband is in good company with many millions of men all over the world. I would talk openly with no judgement about his masturbation. I never met a man who did not masturbate. Find out what he likes about that type of porn. It is said that jealousy and sexual arousal have the same physical effect on men. The only difference is the circumstances they feel it in. So watching that kind of porn over and over will associate those acts as sexual arousal because online the woman is not you and he is not feeling jealous, just aroused. The problem with most fetishes is that they nag at you until done. However, wanting to do something and actually doing it are two different things.
Best thing to do is tell him that you do not mind him looking at porn for whatever reason, as long as it does not affect your sex life. The secret to a great sex life is frank and good communication about each others sexual likes and fetishes. I know a lot of couples that role play cuckolding. The wife will talk about some guy she saw and how good it must feel to be with a more sexually endowed man. That will arouse your husband if he is into that kind of porn, trust me on that. Some wives will use a dildo while telling their husbands about ex lovers and how good and big they were. Some guys like the humiliation aspect of those type of fetishes and if that is the case with your husband, you can tell him that his penis is too small, no matter its size and how it rarely gives you the kind of pleasure you got from ex lovers. Basically you are doing his fetishes without actually doing them. One wife we knew left am empty magnum condom wrapper in their bedroom after getting tired of hearing her husband ask her to have sex with another guy and then tell him about it.
As someone who led a fetish sex life, I hope that I shed some light on the subject and explained the different options you have. The problem is that a kink is something a man wants to do while a fetish is something he has to do. Odds are that he is just mastrubating to that stuff. That stuff requires a wife so cheating is not going to do him any good. Don't worry about it but try to find something safe that you an do to feed his fetish without actually doing it. Many guys are content with just pretending.