My girlfriend told her ex that she loves him, what should I do?

You have to confront her. You'll have to admit that you looked at her messages but she'll realize that she has wronged you too. Her telling someone else that she loves them while being in a serious relationship with you in a classic example of deception. You have to ask her why she did this, if she meant it, how she feels about you, and what this means. I understand if you feel scared. I had to something similar a few weeks ago with my boyfriend. It wasn't as serious as this, but I told him we needed to take a break to see if we should be together. After a week of not seeing or speaking to each other he had realized oh too well how wrong he was and how much he wanted to be with me. This could be the case for your girlfriend, perhaps she was feeling lonely from not seeing you lately and resorted to an ex. However, you have to stand your ground and let her know that it still is not right and it hurt you deeply. Though you're scared and you don't want this to be the end, realize that it could be. If she doesn't love you then it's over. If she does though, you have some major work on your hands. Good luck.

I realize you don't want to confront her, but you should do something. You're only going to get hurt and the lack of communication between you will get worse. You really do need to confront her, and do so honestly. Which means admitting to looking at her Facebook messages, unfortunately. She'll probably be royally p*ssed off, but when in a serious relationship with someone it isn't just about her or just about you. It's about the two of you. Admit that you were seriously wrong and that you really were just curious. See where the conversation leads you.

For all you know she may just be very good friends with her ex. It isn't so uncommon. And it isn't uncommon for girls to tell people other than family and significant other they love them. There're different forms of love, and for all you know this could very well be a platonic love that she feels for her ex.

It's best to be straight and hope that it's a misunderstanding, rather than letting yourself get hurt further.

That exact scenario happened to me just a few days ago. I'm still horribly confused and upset. I don't really know what to do, or how to handle it. He's the only person in 19 years that I've ever loved, and the only person in all that time that I've ever opened up to. It's... I can't get it off my mind, not even for a second. And I want to because we all say things and make mistakes. Well get angry or upset or feel alone and turn to people we were, or maybe are close to, and tell them things that maybe we don't mean afterwards but... Doesn't make it hurt any less, ya know? Well.. Hah, of course you do. I'm guess I"m just thanking you for posting this.