I've been dating Christina for a year. We have been long distance for the last two months, with two more months to go until she gets back from a program she is in.

We often talk over Facebook chat. If you guys don't know how FB chat works, if you copy and paste a photo into the box, it sends it automatically. You don't get to preview it before it sends.

So, Christina and I are talking. She says she wants to send me this funny gif of a dog, and then she accidentally sends me a naked picture of herself, in her bedroom. It wasn't a selfie. She quickly apologized and backpedaled, saying that she meant that for me, but she wanted to send it later, as a surprise. I asked her who took it, and she said she set a self timer on the camera on her iPhone. This excuse especially doesn't make any sense to me, because from the angle it's at, it definitely seems like a person took it.

The weird thing is, Christina and I don't exchange nudes. I've never asked any girl for a naked photo, and she's never asked one of me. Sometimes we send each other steamy texts, but that's the extent of it. I'm also suspicious because the photo was already saved to her clipboard, which makes me feel like she pasted it somewhere already.

Is my girlfriend cheating on me? How do I even find out?

tl;dr: My long distance gf accidentally copied and pasted a nude photo of herself into my Facebook chat. She apologized and said it was meant for me later as a surprise, but we have never exchanged photos and I don't believe her.