A couple days ago my girlfriend was having some serious issue that I couldn't help her with. Her best friend and uncle died on the same day and I was out on a family vacation so I couldn't be there for her. She hung out with some friends that night and didn't respond to my text or call which I though was weird. The next morning she texted me saying that she fell asleep and that she was at a friend's house. We were in an argument the day before and she still seemed mad at me and we were arguing again. All of a sudden she send me a picture of her and a guy in a bed saying he's all she wants. I flipped out and ended the relationship right there. Six hours later she tells me that the she was really mad at me and that the guy in the picture was her friend's boyfriend and her friends influence her to do that to me because they thought it would be a funny joke. She apologized to me and told me it wasn't funny and that she didn't sleep with a guy and it was understandable if I didn't take her back. Of course my foolish self took her back. She told me that she was under the influence of strong painkillers (which she has never done before) and was messed up from all the recent deaths and her friends convinced her to sent the picture to me. I believed her at the time but now I'm a little more skeptical.
1.) Why would it take her six hours for her to tell me that it was a joke? Did she actually cheat on me and realized how much she messed up and didn't want me to feel so bad?
2.) Why didn't she want me back? She seemed like she didn't even care if she got me back or not. Did she feel bad that she cheated on me and didn't want me back because it wouldn't be fair for me?
3.) What would bring a girl to do this? Should I believe her?