<human>: Can you summarize the given text in a few sentences?

I need some advice on how to bring it up. She previously had her blocked then unblocked her and acted like she had not unblocked her. 

I got the call 30 minutes ago from someone who knows all three of us. I do not want to specify what the previous issues were but they were bad enough for this to be a problem for me.

Her (partners) friends list is private and was privatised 3 months ago. I'm inclined to believe this is the reason. She has also recently changed her laptop password (I saw her do it) and yesterday I saw her looking at a picture of her ex when I was walking into our lounge from the kitchen.
She is also spending a lot of time on Facebook chat during work hours which is unusual for her. 
 I would not be okay with her being in contact with her ex and this would be the end of us should I find out it is true. 

When I have brought issues up in the past she has become defensive and it will/has cause an argument. I need a way to bring this up to her without her feeling accused or cornered. 

Is it wrong for me to request to see her Facebook friends list? I would feel extremely awkward doing so but I also feel very low about this entire situation.
<bot>: GF may be in contact with EX although we have agreed no contact due to past issues. I need help on how to bring it up.