Ok there are a couple of things in your scenario that don’t quite scan upfront. You’re friends with this guy and his girlfriend who’s pregnant.
The guy is moody and uncommunicative and won’t talk so you immediately assume the answer is in his email? Which you proceed to hack.
Either you did a much more comprehensive search of his personal shit and came upon this, or you suspected already what was going on and went to the source. I find it highly unlikely that one just assumes that when a friend is in a bad mood complaining about lack of sex, the logical answer lies in his email.
So, I don’t think your situation is as upfront as it appears. Which begs the question of why you felt the need to go behind his back, for what? What were you hoping to find in his email that was going to help him out of a bad mood and lack of sex?
You were looking for evidence. Why? You certainly couldn’t go back to him and say that you know what’s bothering him, and offer to help, because you hacked his email.
These are your choices, not theirs. No matter how close you think you are to these two, there are parts of their relationship you know nothing about and never will. No one tells an outsider everything about their relationships.
In a situation where you are friends with both of the parties in a relationship the only course that works is neutrality. Don’t be the confidante of either. It’s why I insist that my partner has his friends and I have mine, and why I don’t become good friends with his friends. That way we both have people to talk to who don’t have divided loyalties.
Our mutual friends are just that, and we don’t discuss personal shit with them.
So back to you. Does she have a right to know? Sure. He has a responsibility to tell her. He’s not going to probably, though that isn’t outside the realm of possibility.
But what you don’t have the right to do is create a crisis in an already stressful situation. It’s not your relationship. You don’t know what she knows, what she suspects. Maybe she wants to get through this pregnancy before she does anything. Maybe she’s hoping he’ll change. You don’t have the right to assume control over her options, or indeed his. You put yourself in this dilemma. You went looking for information, in an underhanded way. That’s premeditation, you didn’t run into the boyfriend out in public, you went looking.
What exactly is your motivation for confronting her with this? Is that being a friend? Maybe you should keep it to yourself, say nothing to either, and support her through what’s obviously a stressful situation. Don’t add to the drama.
It’s got to be a huge amount of pressure on him as well. He’s really young, he’s most likely extremely unprepared. Can he support a family? Is he mature enough to be a stable influence? What are his motivations for cheating? You don’t know, you don’t have the answers for any of this, you don’t know what goes on privately between them. You don’t know how much the pressures if impending parenthood are influencing their behavior, you don’t know how a child will change them.
You don’t have the information necessary to say whether your actions will do harm or good. You don’t have the right to make that kind of gamble with their lives.
So keep quiet. You can be a friend and a help without ever saying anything about this – just like the friend you would have been had you known nothing. Which is what I would do, forget you know anything, and do your best to help out.
Finally, you wouldn’t be carrying around this secret if you hadn’t betrayed a trust first. That’s yours to carry, your choice, your consequence – and if he walks, or she tosses him, that’s their choices and their consequences, and you aren’t involved in the ensuing carnage.