Is this something I should be worried about?

[327]

I think you shouldn't admit to logging into her Facebook page because if you did she'd start an argument on how you "don't trust her."
You should tell her that you were saying how sorry you felt for her (because she fell off the bus) to your friend. And that he responded with...whatever he said to you about it being a lie.
Then say that you were out hoping to surprise her because she was out "on her own" but you were left disappointed when you saw her with this other guy.
Say it to her face she'll be stuck for words and then ask what she has to say for herself? And if she really loved you why would she lie for attention and go off with other guys and keep it it from you?

I for one think you deserve much better