How to tell him what I found on Facebook?

[A.nice.person]

That's a tough one. Hmm I would say that you happened to see his facebook account up on the computer screen (acting like he had just left it logged into his name) and then share with him what you noticed. Let him know that you were just really bored and having fun because you had n better way to pass the time really. I hope that this helps, it's the best I can really think of. I understand this isn't an easy situation.