I’m hearing a lot of words like “always,” “never”, “NOT”.....”crazy” (lol)
There’s no flexibility here in the posts & it sounds like you’ve already made up your mind....so I’m not sure what you’re asking anymore.

Can a fetish be fixed???
Will he cheat on me bec I can’t sexually satisfy him?
Will this kill him if I leave bec of his heart condition?
Idk. It sounds like you’ve painted yourself into a corner...& he says he chooses to be with you always so.....I really hope it lasts that long.

And an open relationship is certainly not a threesome.