Well it sounds like an absolutely classic midlife crisis. That's very hard for you and sounds awful and I am so sorry OP.
I think all you can do is work out what YOUR hard boundaries are re are all of the issues:
Work/finances
Holidaying
Socialising/drinking
Sex.
And he has to think about what he wants to.
And then you need to sit down and talk about it and see if you can make them align.
For example - voyeurism - does he want to go to sex clubs and you to go with him, not to play with anybody else but just to watch? Would you consider this? (Perfectly fine to say no, that disgusts me, fuck off).
Going out drinking - well yes he should have some chances to do this provided he does not drink in a way that is harmful to himself or others, but equally so should you have social time alone. So how often is it ok for each to go out, what arrangements need to be in place to make it fair. (eg. Put on the calendar a few days in advance so the other one is aware they will be looking after the kids alone - whatever).
You see where I am going. Sadly people do change and grow out of relationships. Clarity and good communication are needed to see if your desired lifestyles are compatible any longer.
At least I guess he is being honest and telling you he wants to try new sexual activities - many people just slope off and do it....
But I am sorry for your pain OP - it's impossibly sad I know.