I don't know if he's gay or not but his kinks show an element of possibly pansexuality or he could be bisexual.
The bottom line in you sound very unhappy with your sex life, and unsatisfied. Having sex twice in the last twenty years would be enough for me. I understand its not always easy to leave though. People are always so quick to say leave but it's not as simple as that financially especially now we are in a cost of living crisis.
I don't know if this helps but I have the same issue with my partner, I always instigate sex and if I don't it doesn't happen. I've brought it up so many times and it never changes.
The whole thing makes me feel v unattractive and I've often thought about having an affair. I've not acted on it. I'm so sexually frustrated I often have sex dreams.
I know the effect it has to always feel like the chaser and it can lead to feeling depressed and having low self esteem. Work on yourself, getting yourself to a place where you feel confident and really consider what you want in life. talk about having an open relationship as your needs aren't met.
Be firm and say while you've explored his fantasies and kinks isn't it time your needs are met too?
If you've already had these conversations how does it go?
Two decades of not having your needs met is such a long time and you deserve to be desired.
If he is bisexual would you stay? You need an honest answer from him or it will drive you mad. If he is bi he can still be in a loving relationship with you but its just a case of whether you would accept that or not?
Best of luck and I really empathise with how you feel xxx