<human>: Give me a shortened version of the text

It seems like many of the infidelities discovered by /r/relationships users stem from reading a SO's text, email, or facebook message. In pretty much all of the threads, that fact is ignored, and the actual infidelity is addressed.

So, does /r/relationships think snooping is justifiable? If so, are there any limits to what can be done, and what shouldn't be done? Also, what are signs in the relationship that justifies snooping?

Here's my story:

In my last serious relationship of 1 year, my SO [26f] was constantly texting her 'friend' who lived across the country. However, she always claimed that he was just a brother, and there was nothing going on. She would text the guy while at my place, and she would talk to the guy on the phone at night, which we didn't even do.

Eventually, I got suspicious and paranoid, and I ended up checking her phone to find her sexting with him constantly, and them sending naked photos to each other. I obviously confronted her, and she was pissed off about me looking at her phone.

However, I find myself pretty jaded lately. I'm currently dating a new girl [24F], and she freely admits that she has two guy friends who are really into her, though she's not interested in any of them. She recently sent me a naked photo, but accidentally sent it to one of her friends instead, and that friend sent her a video of himself jacking off. Granted, she told me about it, and I laughed it off, but I feel pretty insecure about what's going on. I want to snoop to get the peace of mind, but I really don't want to. I felt bad enough last time, even though it turned out I was right. She has been pretty honest about the things she's done in the past, but I really have a problem trusting anyone.

I have no idea what I should do.
<bot>: Under what conditions are snooping justifiable, if it ever is? Also, paranoid about current gf, not sure if I should invade her privacy or not.