Should I be suspicious of my girlfriend?

Me and my girlfriend went through a rough patch over Christmas due to a build up of different arguments, in that time I started to notice that any time I was on Facebook she was too. After a while I started to have a look when she’d go on it and found out it was nearly all of the time.
Now obviously that’s fine and nothing to get paranoid about but when she came to mine for a few days, she only ever went on Facebook when I wasn’t there and hardly went on it at all, she went on other apps like WhatsApp and Instagram around me.
Straight away when she goes back home I notice that she’s back on it all the time, till right before she goes to bed.
am I just being paranoid?
Should I be suspicious of my girlfriend?
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