I've definitely done the snooping thing, but only on the computer & cell phone. And only because I was suspicious. After barely two years and his level of affection decreased sharply - I wasn't gonna take that lying down. Anyway, I found conversations with other girls where he told them he didn't have a girlfriend, and they were flirty and sexual (and then he doesn't flirt with me like that anymore). Moreover, they sound like the conversations that we used to have when we first started dating. I confronted him about it and he said he would never actually cheat on me but he just wanted to know if he was still in demand. I broke down the first time I found a convo like that and I thought he understood, but then I found a second conversation that was even worse than the first. And then I found a text on his cell to the second girl that asked her to be his valentine. On Valentine's Day! He said he was just being nice and that she had a boyfriend. Oh man, ladies, I hope you never have to deal with this, because he doesn't understand that it broke my heart.
Hope that answered your question =)