Re: do all men cheat?
If by opportunity you mean Kate Upton on a secluded island, shirtless and telling a man to “aj lut le jo lutna ae” then probably more than 95%, but to be fair anyone who is not actively looking for an opportunity is very very unlikely to cheat.
I only know of 2 men in my circle who have cheated. The rest have not even when there was ample opportunity for someone who was looking for an opportunity to cheat.