"I thought he trusted me enough to tell me things like these"

"I just want to go out of the house for tonight and not see him for a few days"

These sentences don't add up. Your husband clearly has good cause to keep aspects of his sexuality private.

...And that's his prerogative. We don't own our partners. People are allowed to have private fantasies. Not everyone wants to bring up their kinks. Some people might be ambivalent about their desires and prefer to keep them away from the relationship. So long as that stays in the realm of solo exploration, I think that's fine.

The photo sharing could approach a grey area, though, depending how he's doing it. That's probably what concerns me more. If he's soliciting comments / DMs that is not really "solo exploration". If he's showing his face... that starts to feel personal. And if his posts are including any personal info pertinent to yourself - e.g. identifiable images of your home, names, info about you or his location, job, workplace etc. - that would cross a line and need to stop. Even if that means revealing you saw his Reddit account.