Whatever your excuse is, everything is hugely dependent on exploiting trust. That sounds bad (because it is), but it's also the brutal truth.
Like once upon a time, yours truly was supposed to be hanging out with my best friend and then ended up spending the night at his place because of a migraine. The reality was that, uh, I was catching up sans vetements with an old and very close female friend (that I should have married). But trust was there in that relationship so I got away with being a scoundrel.
But once the trust is gone (assuming you play the field with a civilian or service provider, get busted but she stays with you), you're on a short leash for what seems like forever.
A good friend of mine had a 7-year long affair. He met the side lady not much longer after getting married. He left the house for years under several ruses and even went out of town with no issues from his wife.
Then one day, his crazy side woman befriended his wife on Instagram and sent the wife pictures of both of them hanging out in San Francisco. Somehow, he went to counseling with his wife and they worked it out and didn't get divorced. But he can't do anything now. He can't visit his mom in San Francisco or hang out without suspicion raining on him. To further complicate matters, crazy side woman is still texting him naked pictures of herself! Fortunately, the odds of an SP ratting you like this woman did are low, but the moral of the story remains the same: don't get busted (or possibly don't be a scoundrel but life is too short to be a choirboy).