I'm sorry but he likely planned to cheat when they booked the stag do.
They pick places like this specifically to do it, sorry but men, even the ones that act the good act and talk the good boy talk are all vile if they can get away with it.
Look at how he's lied to your face and been completely normal for 6yrs op, he didn't give a thing away did he, not until your recent health scare where he felt like his dirty secrets would be discovered.
It's like when celebrities get discovered doing something by the press and they have to come out and address it before hand, they do that to control how much information gets disclosed, so they can downplay the awful things they've done.
Same as your filthy husband, oh he can't remember, oh he feels so bad he blocked it out.
Nonsense! He knows, he's always known he just has no respect for you so won't be honest about how disgusting he has been and how vile he has been to you, he also wants to protect his image, once you know EXCATLY what he has been doing then you could tell everyone he actually does have respect for like his family and your mutual friends, he will lie to you to stop this from happening.
He's just a disgusting lying piece of shit who has probably put your health at risk numerous times over the years, I'm so sorry.