How should I respond to this "flirting"?

I’m not exactly sure if some would call it flirting considering it’s online and all, but I stumbled across these messages when my g/f left her chat from Facebook open on my computer.

I didn’t purposely go snooping, it was just already there on my screen when I opened it, and this is the only part I actually read. I didn’t want to go further into it because I would have felt bad for snooping.

I’m usually OK with harmless flirting, but these seems a little further across the line. Is it wrong that I feel bad/jealous? Should I confront her about it?

As a little history: She has done some serious flirting (near sexual) with her ex online before. Stated how she wished she was there with him and such. My brother actually brought it to my attention because it was on facebook, which I don’t use. After confronting her about it and ultimately having to give her and ultimatum (Stop or I’ll leave because I feel completely disrespected and betrayed), she stopped flirting with him.

Anyways, here are the messages:

Her: Hey sweetheart how are you today?

Him:<333
I wish you could come cuddle with me and rub my back for me. thanks sweetheart your the best

Her: I would if i was there to help you feel better

Him: Aww i wish you was it would make me feel like a new man.