Is my mom cheating, or am i just being paranoid?

Well, it sorta all started out like a year ago. My dad had taken some private golf lessons and my mom, me, and my brother did too, when my dad suggested that he was good. Well, for some reason, my mom just got involved in talking with him. She would text him all the time, like everyday, and they haven't known each other for very long. He would always tell her his personal problems, and when she told me some of what he told her, she would always say,"Don't tell your dad." i would ask why, and she would, kinda hesitantly, say that he would think its weird, but for some reason i didn't believe her. And then one day i told her he had a Facebook. She acted sorta surprised and i guess happy. So she started getting onto Facebook a lot (and she used to never care about it). Now, when she gets on, she wont let me see what shes doing on there. She'll turn the phone away so i can't see, or she'll sit in a corner when shes on her phone. :( I need to know. I think i'm just being paranoid about it, but i wanna make sure. I don't wanna ask my dad if he noticed anything, cause i don't wanna make him worry. My mom once told me that dad had asked her to stop texting him, and she got sorta like annoyed. Not really mad, just....annoyed i guess. Ever since then she hasn't told me anything about him. Every once in a while she'll talk out loud and wonder if hes doing all right. Ugh....I'm so annoyed. Does she like him, cause she would never, not that i know of, call him or pretend to be somewhere else. I don't know. I think I'm just being paranoid?......