perhaps he has genuinely lost his sex drive because he is tired and stressed from work.
as for the lap dancing, he was out with his mates on a stag night and probably felt under pressure to join in and have a dance.
i used to go to lap dancing clubs all the time, there harmless fun and your not allowed to touch.
forget the lapdancing completely, its irrelevant, have a good amicable chat with him and see whats up.
you say you have a high sex drive and are adventurous, if i had a wife like you i wouldn't need to even think about straying so find out whats the underlying cause, dont throw your marriage away for nothing.