Talk it Out
I imagine you are correct, that a conversation with Abby is important. It sounds like you *could* be having issues with her new found interest in showing affection to other guys, this might be a good place to start. Otherwise, giving her the opportunity to talk to you about what is going on with her (if anything) needs to happen.
With any luck she will dive on the chance to express her feelings. Maybe an open type relationship is not for her and she needs to make an exit. Maybe she needs a different level of communication with you. Maybe there isn't anything wrong and she's just going through a change and the issue is yours in dealing with it.
In the end, playing guessing games is the path of monogamy (in my opinion). I no longer shy away from expressing my feelings and my partners should feel free to do the same. I'm willing to help a little bit to get them to open up, but sooner or later they are going to have to figure out how to talk to me.