Yes, I had a gut feeling about my husband before I had any indication or proof. I noticed that he seemed more stressed, tense and angry. Very high levels of this. In addition I noticed him distancing himself more from me and being more critical of me and the marriage.
I don't think all spouses in affairs necessarily do this. I think some can probably deal with their guilt more easily or hide it better. Also, I think those who want to keep their marriages together, or who are better at hiding things probably don't display that anger. My guess is they might even be nicer to their spouse to take off any suspicion.
My only "indication" in the beginning was him staying out one night until around 2 a.m. and then actively hiding his cell phone. My "proof" was hiring a detective agency to get cell phone records and seeing an unusually high amount of calls to one particular female.
There is no arriving, ever. It is all a continual becoming.