Girlfriend likes pic of a guy she "hates"?

Here's some background information:

So me and my girlfriend had a fight about this one guy who is my best friend. This guy was the guy she liked before she even noticed me (she didn't bother talking to me). He didn't like her though. She's saying that he's trying to end our relationship by saying things that he wouldn't have said like "Just break up and move on". She is saying he's trying to end our relationship because I spend more time with her than him. I'm thinking that she still likes him but doesn't want to show it so she wants me to tell him to not hangout with us anymore. It scares me because she liked him first before she liked 3 other guys and then me and this guy is the one we hangout with. She has liked most of his selfies while we were dating.

Anyways, she liked a picture of him with his shirt off at the river. This was the day after we had a fight about him. She's been saying all this crap about him and then she likes his picture. Help me guys! Thanks in advance.

NEW: So I talked to her about it. She says she liked it accidentally and didn't want to unlike it because that would be rude. She promises that she loves me.