Is she cheating?

I don't know where this topic goes. But I don't know what to do with my mother. This is her 3rd marriage and the other two she has cheated and I'm suspecting her of cheating in this marriage. For example, she's up hours of the night on her phone. Also, she ALWAYS hides her phone from me, her husband, anyone that lives in the house like, always. Putting her phone down so the screen so it isn't facing up, always on her messages, and won't let me hold her phone either because of notifications showing up if she wanted to show me something. Who knows. I know it isn't my business and I shouldn't do anything to look into this more but I need someone else's thoughts!